They will stay.
Anyway, all speculations aside, this is what I would do this summer. I've already said some of those things over the past few months in different threads but here are now all at one place.
GK: Bravo, MATS, Masip/Ortola
Reverse Bravo and MATS roles and promote Ortola if Masip leaves. If Bravo won't accept his new role and wants to leave then Reina probably wouldn't be a bad choice for 2nd GK if he wants to return home.
RB: Alves, Vidal, possibly use Roberto there as well; sell Adriano, Montoya and Douglas (if possible)
I'd continue to play Alves in big games where he's still fully motivated. Give Vidal starts against worse teams in first half of the season and then see how he plays. If he starts to overplay Alves then reverse their roles. We absolutely should see what we have in Vidal before giving up on him and sign new RB.
CB: Pique, Masche, Mathieu, Bailly/Umtiti, Lemos/Mere/??? (on loan); sell Vermaelen and Bartra
I know Bailly better so I prefer him, but would be happy with Umtiti too. Although a small sample but Bailly has also played good at both RB and LB for Villarreal against both Madrid teams so maybe he could be our 3rd option at either FB positions in case we need him. Certainly can't be worse than Adriano or Douglas.
I don't think we should waste our time with Marquinhos/PSG and Laporte is as good as gone to City. Also buy another young CB and loan him for a year to get more La Liga experience then return him next season as possible Mathieu replacement. Also give some opportunity to Tarin or maybe Borja Lopez in CDR games and final groupstage game or two of CL if we are already qualified.
LB: Alba, ???; sell Adriano
Guerreiro is the latest rumour and although I don't know him good he could be a solid option for around 15M. Adrian Marin is a good talent but still too inexperienced for my liking but there really isn't a good LB market out there. Anyway, we don't need a new starter or WC player there but just a solid rotational player who can give rest to Alba and compete with him better than Adriano or Mathieu, so there is no need to pay 30M for Ricardo Rodriguez or Wendell and I'm sure we won't do that.
DM: Busquets, Roberto
I believe Samper will be longterm Busquets backup and maybe his replacement some day but he needs regular playing time in La Liga before that so loan him out. Roberto can cover up good for Busi next season.
CM: Iniesta, Rakitic, Arda, Denis, Rafinha
I know some fans want new midfielder beside Denis but I'm happy with that group and don't think we'll change anything. If we buy midfielder, I'd prefer someone like Bazoer. Get him and make him our Pogba for 4-5x less money. Also give a chance to Kaptoum (if he won't go on loan) and maybe Alena in CDR games.
RW: Messi, Rafinha/Arda
Messi plays always when he's healthy and that won't change anytime soon so there is no need to buy a replacement for him (he's irrepleacable anyway). We should cover with players we have when he's not available.
CF: Suarez, Gameiro (Munir on loan)
I've already said why I prefer experienced backup over youngsters. Suarez played too much this season and we're lucky he didn't get injured before. We should reduce his minutes for 1.000-1.500 next season and for me Gameiro is still the best available option to replace him.
LW: Neymar, use Denis there as well
Not much to say. I think Denis can give Ney a rest when needed.