The space plane ideas for using a Sabre engine are fairly early stage designs, since the whole engine isn't even a working prototype yet.

Of the various designs I've seen via wikipeda, Reaction Engines PR, and on-line forums, it seems that the thermal management proposals are :-

* Bigger lighter air frame will do more thermal soak than other spaceplanes (I mean, what else is there apart from Shuttle and X15?)

* Retain some fuel to be circulated through airframe during decent, and then used for powered landing

* Less intense re-entry profile to avoid sharp heat spike, but at expense of longer thermal load

* Avoid going all the way to orbit, using a small final booster for orbital insertion

If they can harvest enough LOx/air in the final ascent, then they could also do a retro burn I suppose.

Perhaps a mix of all these, plus heat shields. SpaceX are learning how to deal with similar issues right now too.

> what else is there apart from Shuttle and X15?

Buran, X-37 .

And soon hopefully Dream Chaser.

maaaaaybeee it could save enough fuel for a reentry burn?

No chance. This is more like maaaaybe single stage to orbit, though it wouldn't have a very big payload.