And note more generally that you can’t get a BP without an e-ticket, so once you have the BP you’re good.

Of course it’s always possible that an e-ticket can be revoked after issuance of the BP, for example if the booking is cancelled, but that’s more relevant in disruption etc.

It’s when you can’t get a BP in the first place that it can be a worrying sign of an e-ticket issue. (Or one of many other things…)