Ticket barriers don't generate information which is then automatically visible on internal emails / TyrellCheck [internal software] etc. Therefore a member of staff has to report it. Sometimes this will just be to locally affected stations (eg. a phone call saying "hello St Pancras, three passengers will be arriving without validated Oysters or any tickets"), and sometimes it may be reported to Control and then broadcast by emails and so on.
If you have to argue your way out of the barriers, it's unlikely all staff have got the message. A plausible story about a regular fault may be enough to let you through, but it's not worth relying on. As above, you should make an incomplete journey and then deal with it later - check if it has been completed automatically, and if not, use the online TfL account handling to log an enquiry, or call the number which is printed on the back of every Oyster card. The time penalty will likely be no worse than if you'd been making a journey where you'd needed to buy a paper ticket at a ticket office or TVM. Most of the online Oyster / contactless tools are quite reasonable in terms of ease of use - as they should be, given the volume of people who use them, and the work accordingly put into the software.
As for revenue staff (or Passenger Hosts, as Thameslink now call them) - they should be approximately aware of revenue equipment issues, via their company-issue phones, but may need to check them if they haven't seen a message but need to verify it. The same applies to gateline staff (whom you probably encountered - to be fair, they would be less likely to detain you until they had proven that something is actually out of order), and it's worth pointing out that outside of the busiest mainline stations, the screens mounted by ticket barriers are usually simply for controlling the gates themselves, and not actually accompanied by any display which shows customer service information. The phone may be in the pocket, but it would be silly to expect it to be practical to constantly be staring at it, waiting for random emails about TVMs and ticket barriers to come through. So staff may need to check it specially - and it may be down to their perception of the passenger as to whether or not they think that necessary.
If a member of revenue staff did check tickets at any point, then when it comes to checking Oyster, the handheld readers will flag up that you have not touched in, even if you have reached your cap for the day (credit levels and precise deductions are not shown on the readers currently used). They also do not know about local stations which might have problems, as the system is not quite that clever yet. So you would likely be asked about your journey and at best you would be delayed whilst the revenue staff checked with your origin station to see if your story was correct; at worst, you might be issued a Penalty Fare and have to sort out the journey problems later - not ideal at all, but I'm not discounting it could happen if no report of the issues had yet been transmitted. Obviously this element would not be your fault. The really tricky bit would be if you were seen to be trying to exit a station without touching out, and it was subsequently discovered that you had not touched in either. This would mean you were effectively trying to get away with no record of your journey being made, and regardless of whether the origin station had been having problems with their equipment, you could be issued a Penalty Fare or reported for prosecution. Being capped for the day on Oyster/contactless would make little difference, because this is an arrangement which does not override the need to get a valid ticket at the first opportunity. A capped Oyster or contactless card is not a valid ticket by itself.
As for contactless, your journey will be started, and a maximum fare potentially charged, if you are inspected on one of the handheld readers, having not touched in. This is a measure to counter misuse, to ensure that if your ticket is checked, it isn't cheaper to just have a contactless card which is tapped on a reader every so often during a ticket check. Because these readers can only tell whether or not a card is authorised for use, a card which is only used once or twice without valid touch ins / touch outs will still pass the authorisation test, but still needs to be charged in absence of the back office system actually knowing where it was used.
Should you then touch out with your contactless card, there will be a reference point for where your journey finished, so you should be able to later reconcile the start and finish points of your journey by use of the online tools or the phone system. If, however, you do not touch in or out, having been inspected by a handheld reader on the train (or at a station) your card will be marked as having been misused, and the maximum fare charged. TfL might refund the difference between the maximum fare and what you should've paid, but so far as I have been informed, this is not guaranteed. In addition, you would need to make sure the misuse is removed from the card's history, as too many incomplete journeys on contactless will result in the card no longer being authorised for travel.
