Is it not working or just not turned on?
Is it going to make a return any time soon?
Which would seem to exclude this incident from the RAIB's remit. It is also almost certain they would have published a news story about it by now had they been investigating. News reports from the time talk about investigations by the BTP and ORR, but not the RAIB (or HSE). Neither organisation has made a public statement on their website that I have been able to find, and there are news reports later than a couple of days after the incident so it seems very unlikely the investigation has concluded. It is quite possible that one or both organisations have asked that the travellators remain out of use until the investigation is complete (and at that point it seems likely to me that the apparently routine maintenance that was being undertaken will still need to be done).Certain other railways are specifically taken out of the RAIB’s scope by specific regulations within the 2005 Regulations. As a result, the scope of the RAIB’s investigation does not include:
[..]
worker accidents or incidents that are not associated with train movements and which are not relevant to the operation of the railway (Regulation 4(6));