Have had exactly the same dilemma as you as I've also just relocated from London to HK (and strangely I also have BA Silver and BD*G). I decided to sit tight for the first year (and of course, you never know, it might be the last year....). You've got your flights back to the UK which as has been pointed out you could take on BA and which would get you 480/600 TP needed to retain Silver if you fly J. You don't say whether you're flying full-fare Y on the other Asia routes. If you're going on a heavily discounted fare then you won't get the BA TP which could leave you short of retaining status.