Is the end of our house about to fall off?

A surveyor came today to look at the house on behalf of the buyers. It seems to have worked out ok but we were worried for a while. You see for some time now a crack has been developing in the plaster running floor to ceiling in our bathroom, just at the point where we have a full house extension. The crack seems to be confined to the plaster and not the outer wall, but it does seem too much of a coincidence that it's where it is, and who says it won't develop to the outer wall?

Anyway, it's not very ethical I know but we did a patch it and paint it job and the surveyor never seemed to notice it. I just hope to God the buyer isn't sat in the bath one day in the future and then suddenly find themselves bathing in the garden surrounded by rubble!