Can you verify this? Anything I've found, including stuff from McGill's own website, seems to suggest that the bulk of the money came from Percival Molson's own estate in accordance with his will, with no indication of any stipulation that the stadium be named after him, and doesn't give any other members of the Molson family as donors. I can't find anything at all about McGill trying to get rid of the name. I can't even figure out how Percival is connected to the rest of the Molson family.
In any case, the name doesn't appear to be a corporate name in the modern sense, where corporations pay for naming rights and the names last only as long as the corporations pay, even if the money did come from the Molson family.
I could see Molson fighting against changing the name, since it amounts to free advertising for them.