London to Oxford Sat May 13: best option now?

Point 1- The transfer on GWR train to bus at Didcot is easy. The bus stops at the station entrance, is well signed and lots of staff around to guide you. It's a nuisance, but not a big deal in terms of difficulty.
Point 2- Yes Chiltern will take the ticket.
Point 3- Victoria is the same journey time as Paddington, from St Pancras, on the Victoria Line.
Be aware that the Oxford Tube departs from a stop on the road between Victoria Rail and Coach Stations- not the Coach Station itself, and it is a flat route all the way so you can roll your case all the way (I do it quite frequently). It is well signed, and there should always be a bus waiting there. One road to cross, which has 'dropped kerbs'. On the way I usually use go into the shopping centre above Victoria Station (which is on my route), use their restrooms and get myself a picnic at the Sainsbury's food store in the centre.
You can afford to take the long view on this as the Oxford Tube is a turn up and go service. You can book, but not necessary. So if or when it is announced that no trains are running take the Oxford Tube. If it happens then at that point you can apply for a rail ticket refund.
If trains do run stick to the train.

The only thing I have to add is that you can also use the regular local buses from Didcot to Oxford as well as the dedicated rail replacement ones, with your original ticket. These are Thames Travel X2 and X32. Check whether these may get you closer to where you are staying.

although National Rail and Chiltern have not yet addressed the RMT strike on the 13th, Chiltern is one of the 16 rail companies affected by the ASLEF strike on the 12th and I expect that they will be one of the 14 companies affected on the 13th.

If trains do run stick to the train.

Thanks isn31c. And if the trains run, does it make sense to stick with GWR from Paddington rather than go to Marylebone for Chiltern Rail? Maybe it is easier to go from St Pancras to Paddington than to Marylebone?

These are Thames Travel X2 and X32. Check whether these may get you closer to where you are staying.

Thanks Marco. I am staying on High St so I am guessing X32 to City Centre is better than the rail replacement bus to the train station. Though I am not sure if it is a big difference.

Patty,

Yes, GWR is better for you. Direct train, where's Marylebone is a walk round the corner to Baker Street. GWR is likely to be quieter as most folk will likely be going Chiltern.

On past experience, the number of trains to/from Didcot per hour has remained fairly high during RMT strikes - typically around 50% or better during working hours although they are at different times from usual. Of course we won't have these timetables for a while yet to be sure. Your main problem might be being too late for the last service.

The Oxford Tube will book up during strikes so if taking this option don't leave it to the day.