So he's most likely not coming back to Barça via our buyback, unless we make some kind of deal with Las Palmas.
I could be wrong but from what I've understand from Las Palmas SD words ("Barcelona have a right to buy, they had it with Hamburg, but while we are in the loan period, the clauses can only be executed by us") we can still execute our 12M buy option in 2018 (and 2019 too I believe) even if Las Palmas buy him. So only things that change for us are that we can't bring him back this summer (which wouldn't happen anyway) and if we decide to buy him back we'd have to pay to Las Palmas instead of Hamburg.
I think a favour or good will from Barça that Toni Cruz talked about is just that we'll let Alen stay at Las Palmas for at least 18 month (let's imagine a crazy scenario that Alen explodes over the next few months and scores 10 goals and/or gives 10 assists and maybe if Las Palmas qualify for Europa League they are guaranteed to keep him for another season) and then maybe we'll also pay (let's say development fee) to them if he'll improve enough that they'll decide to buy him and we'll also be willing to bring him back. From Barça's standpoint it's the same whether we pay 12M to HSV or Las Palmas but if this move will help us to fix our relationship (which was apparently somewhat broken last summer when we were trying to buy Lemos) with Las Palmas and we could get Alen back in 2018/19 as a much improved player and maybe also buy Lemos (they also have a couple of other interesting players but I dont think we are seriously interested in any of them) then I'm all for that.
It's not ideal to pay 7M for development to other clubs and I'd prefer if Halilović would just be loaned to Las Palmas last summer but it was Alen's and his entourage decision to go to HSV. Robert probably also wasn't totally convinced Alen can make it at Barça longterm so he decided to at least get something for him instead of loaning him for another season or two (after he was benched for the second half of last season in Gijon who knows what could've happen to him in another club) that could even lower his value if he wouldn't develop as expected.
But if we can get improved, better and more experienced Alen who could be at least a good squad player for us back for 7M of additional fee then I'm ok with that. And If he fails to impress even now at Las Palmas at least we've already gotten something for him. Let's say that we''ll buy Marlon or that Bueno kid with those 5M we got for Alen. I'm ok with that.