If minicabs are going to be difficult because of the tube strike, I'm
coming round to the idea of getting buses to Paddington as early as
possible. (Then HEx).

I agree - with the possible gloss that I'd possible make that "as late
as possible" - ie if possible

a. cancel the room in King William for the night of the 29th;
b. spend the money saved on the room in the bar, staying until as
late as possible (which may be very late if there are others in the
party still resident?);
c. stroll out to the 55 when the rest of the party insist in calling
it a night;
d. reckon on getting to Heathrow absurdly early - but also in good
time to drink lots of coffee to counter the effects of (b).

Of course it may not be easy to judge how much beer at (b) is enough to
cater for the trip at (c) but not excessive (bearing in mind there are
no toilets on London buses!) Perhaps a rehearsal or two of stage (b) at
least would be advisable in the days running up to 29 June?

PS
Thanks to the OP for pointing me to the King William. It is more than a
stroll away but it comes recommended by neighbours too so I'm looking
forward to trying it over coming weeks.
--
Robin
PM may be sent to rbw0{at}hotmail{dot}com