I think the biggest hint that sansa will survive (at least in the show) is the fact that D&D actually invested some time / development in her character arc.
Sure GRRM might plan to build sansa up first so her death is more shocking / impactful (also I think that would actually be quite cheap storytelling). But D&D clearly don't think / write this way. Just take a look what happens with characters / story arcs that have no significance to the endgame (dorne, fAegon, stoneheart, rickon). Just look what happened to stannis .
If D&D don't need a character for their endgame he gets killed of or at the least isn't honoured with character development / screentime until he reaches the point where his death serves another characters arc (ohhh, rickons powerfull dialogs in season 6 ).
Sure D&D also build up some characters to make their death more impactful (karsi, shireen), but they don't put that over the arcs of more important characters.
With sansa it is actually the other way around: they push back undeniable more important characters (jon, arya) to establish sansa as a "badass" (if she actually is one is another question). Like when they needed jon to fuck up the botb to have sansa "save" him.
Here some examples from season 7:
Cogman stating that he intended the jon sansa conflict in e2 to illustrate how jon doesn't include sansa in his plan so she needs to argue in public.
Sansa warning jon about cersei attacking the north (which seemed moronic at this point) in e1 and jon ignoring her warning (guess what happens in season 8 ).
Tyrions "she is more intelligent than she lets out" in e3. Sansas "ruling skills" from e3 (veeeery subtle D&D).
Both D&D and sophie turner were quite vocal about sansa now being a "big player" / politician in their interviews (classic D&D tell-don't-show-principle).
It can all be summarized in D&D not being able to establish a character as important / intelligent without hurting another characters arc or dumping him down.
And in regards to sansa we have multible examples of other more important characters (jon, arya, littlefinger) being dumped down / pushed aside to establish sansa as a "player of the game".
Now both GRRM and D&D could simply build her up to fall deeper. But personally I think that GRRM is to talented and D&D not talented enough for that.
If that is their goal than D&D might give her an emotional moment with arya before it happens (stannis & shireen style). But they wouldn't sacrifice so much screentime on a character that dies of without any impact to the endgame or the story in general.
Regardless how things play out in the books (or what the outline says): we have to keep the D&D-logic in mind when we make predictions for show sansa.