Unless UD drops its last 2 games and falls out of the Top 4, then the only way UD and URI could meet is in the semis or finals of the A10 tourney. If that happens, then Dayton is IN, regardless of the outcome of that game.
And the 8th rated RPI conference is not considered awful, either. That position (8th) in the RPI conference standings usually puts multiple teams (3) in the tournament.
I understand what you're saying about them sweeping UD and the committee not "jumping" UD over URI for a selection. But in this scenario, it's moot, because it's very unlikely the cards would play out that way for such a decsion to be made.
Let's put it this way. If URI wins another game against UD this year, then that's good for the A10, because the conference would be getting 3 bids to the tournament.
As for the Marquette win, I'm not sure what the relevance is of your post. An if you do a little math, even if Marquette loses both of their remaining games, they'll still have an RPI of better than 30. If the lose at Pitt and win at home vs Cuse, their RPI ends up at 22. So much for fizzle.