You are almost certainly right on both counts, but I'd say there is a slight possibility for him signing a shorter term deal.
His QO, of course, is an option, and there is some potential value - although a lot of risk - to signing a 2 or 3 year deal that allows him to re-enter UFA with a higher cap (while still being squarely in his prime). Then, he can sign a 7/8y year deal that takes him til his late 30s, rather than early/mid. If he drops off at say, 33 or 34, he could earn himself a lot of extra money.
I do not expect this to be how things go, but it's a possibility.
Matthews and Aho are such a different level of player, and so unlikely to move, it's almost not worth considering. If either of those guys are dealt, it would be an extremely unique trade and one that has little bearing on Debrincat.