This needs to be resolved within the next week or so one way or another. It benefits neither club having it drag on all summer. Sanchez needs to come out with a statement categorically stating he's either staying or he wants to leave and come to us. If it's the later it's then for us to go to Arsenal with a bid and a deadline, either accept it before the deadline or say no, force him to stay and lose him on a free next season.
If Sanchez doesn't come this summer we then have to decide whether to stick with what we've got, keep Kelechi and go with Aguero,Jesus,Kelechi, Sane,Sterling and possibly Roberts as our attack which last season wasn't enough and was very wasted. However, with Jesus here all season, Bernardo in the middle, helping to create even more and new fullbacks that suit the system maybe that'll be enough and we can wait for Sanchez to come on a free in 2018, or do we look elsewhere at the likes of Dembele which will probably mean no space for Sanchez in 2018.
One way or another it needs resolving soon, ideally before pre-season but that's probably pushing it now.
If i was Wenger and had the approval to keep Sanchez and let his contract run down and lose him on a free next year if need be, i'd be stringing us along all summer as much as possible, might not be great for their fans but it could derail our preparations if we're led to believe we can get him and wait it out.