He isn't going to get doubled in the NBA. So that issue is irrelevant.
Collins is somewhere between 6'8 and 6'10. He is fairly athletic, but not the type of athlete that wows you with his explosiveness. He has the ability to potentially expand his jump shot out towards the 3 point line, but is not there yet. And he has shown no indication he has the foot-speed or lateral quickness to guard the perimeter for any significant stretch of time. His body will probably top out at 250 or so.
I say all that to say that while I think he is a first round pick, he is likely a 7th-8th man on a good team or a starter on a bad one. I guess he could play some small-ball C, but mainly he would be a PF who can get you baskets if you get it to him in the post but is a sieve when asked to guard repeated PNRs or defend small-ball 4s. I would be shocked if NBA teams saw him as a potential all-star or even a top 3 player on a good team. And that isn't going to change from this year to next, unless he shows back up to school next year and shoots 36%+ from 3 on good volume. I can't imagine that is likely, either from his abilities or where he will be in the offense.
If he is given a guaranty, he should (and will) go. If he lucks into a good franchise, he can win games, develop, and be in a position to make $8M-10M/year on his 2nd contract.
The NBA almost never wants you to stay in school to improve your game. People need to get that.