They'll pull the purchases ... until the point when there's a further crisis in which case they'll have to step in again!
But it looks like the govt may u-turn on more of the "mini-budget" fiasco. If they reverse / delay more of the tax reductions this could provide some support to bonds / GBP until the 31 Oct. At which point they present how they are going to balance the books.
RE: Will the BoE really stop buying UK government bonds?