The new deal is a 40% increase over the old one that was $5M a season -- So the total for the league is $7M annually; split 15 ways it's $467k a year; when Loyola joins next year it becomes a 16 team split.
C-USA's deal paid out $750k per school prior to expanding to add Delaware; meaning they are at around $7.5M annually but it would only be split 12 ways; that assumes there is no increase for the addition of Delaware (and presumably UMass).
Basketball credits in C-USA are pooled, whereas the A-10s are predominantly owned by the team earning them. Meaning there is little additional revenue there for UMass, which has earned zero credits in the current pay cycle (and only one since Bruiser Flint left as coach), they would make a bit more in C-USA sharing in the money earned by FAU during last years run. More importantly to their athletic department, they'd finally find a home for football and at this point the reality has struck UMass, they aren't going to be able to do a football-only deal.
I think short of a donor/alumni/fan-base revolt they're gone.