Our booking engine at tickets.railforums.co.uk (powered by TrainSplit) helps support the running of the forum with every ticket purchase! Find out more and ask any questions/give us feedback in this thread!
I would make sure you get the Thameslink to St Pancras and walk to Euston, preparing for a *very* busy carriage between Blackfriars and St P! This will be far easier than having to cross London by bus/taxi/whatever-of-the-Victoria-line-is-running.
The strike doesn't start till 2130 officially.
Southern engineers will be banning overtime on the Sunday, not sure that would have an immediate impact.
Don't know what sort of ticket you're travelling on but changing at Clapham Junction, Watford Junction and Milton Keynes has a time penalty of only around 20 mins on the official NRE cross London connection. It would almost certainly be quicker than the Thameslink trundle through South London and the walk down the Euston Road.
Thanks everyone, I'd thought of the St Pancras option but forgot about the route through Chelsea, I'll have a look at that. I'll probably get an off-peak return which should be fine for that route.
I wasn't too sure if an engineers strike would have an immediate effect on services, I'm going to gamble and assume it won't