Going back to June 1990 --- the FIRST move that was made in the expansion re-shuffle was the B1G inviting Penn State.

But that vote was close. Penn State only got in by 1 vote.

What if one school changed their vote from "yes" to "no"?

The Big East announced in February 1991 they would start sponsoring football. A B1G-rejected PSU is now an option - I'd posit that PSU gets the invite instead of their fellow A-10 member Temple. In the immediate short-term, PSU would keep Olympic Sports in the A-10 as to not disrupt the Big East basketball cart. In the longer-term, PSU Olympic Sports join the Big East (as happened w/ WVU & Rutgers, beginning in 1995).

For the rest of the 1990s, that makes for a stronger Big East - the ACC/Big East "reckoning" likely still happens in the early 2000s, but the Big East is in more of a position of strength. Not unrealistic that teams would have gone from the ACC to the Big East (e.g., Maryland) as opposed to the reverse.

Meanwhile, the B1G --- it's a considerably more regional and insular conference during the 1990s. Any expansion plans to the East are pretty much blocked by a more powerful (than in real life) Big East. Any expansion plans would have to go West - maybe they get a couple Big 8 teams instead of all Big 8 teams joining into the Big XII.