(Just for the record, I have never argued that Nicholls was an all-time great, and only recently I posted on here that I don't think he should be a Hall of Famer -- a topic raised by someone else -- whereas a couple of other people on here think he should be. So, I don't know where you guys are getting your information about me, but it's not from me. I'm not even that big of a Nicholls' fan.)
I think all Oilers' trades from 1987 to about 2004 are what they are -- money-saving deals with a bit of hope for a good player, though that was a lesser concern.
It's easy to understand why Messier left in 1991---which, by the way, I think was just about the right time (whereas I think Gretzky left two or three years too early). For one thing, Mess was ready for the "second act" of his career and a new situation. I think that's quite natural when several of your peers and friends (Coffey, Gretzky, Kurri, plus several of the 1979-era guys he came in with) have left town for greener pastures. The other thing is obviously money. The Oilers simply couldn't afford to pay him what he was worth. I mean, what was he making in 1990-91---like, $600,000 or something? He was 30 and had had some serious injury issues that season (the Rangers refused to contract him until the team doctor cleared him, so worried were they about this). So, I mean, if you're recoving from injury, seeing guys you came in with retiring, and you're making $600,000 but worth $2 million on the open market, one can hardly blame him for wanting to try a new team.
There was always a thing with Doug Messier (Mark's Dad) and Sather, during training camp, from around 1986 to 1990, where Mark would hold out while his Dad negotiated with Sather. And I think, by 1990-91, the Messier camp was tired of having to spend weeks hammering out a contract every year that would pay Mess less than he was worth.