You have to distinguish among three things, though they are all closely related: 1) the number and health of the schools, 2) the health of the PCL as a multi-sport league, and 3) the health of the PCL with respect to football.
Re #1: As I understand it, there will be no closings for at least a couple of years, but unless there is a reversal in long-established trends, (e.g. more Catholics begin deciding to send their kids to Catholic schools) it is hard to imagine there not being 4-5 fewer schools in five to eight years. If that happens, there could be some mitigation by bringing in Shanahan and persuading Malvern to join but you're still looking at a shrinking league.
Re #2: The league works well for basketball, soccer, and baseball and OK for some of the other sports--probably better for most other sports than for football. In a few sports (e.g. swimming, rowing, golf) many schools don't compete and there is a very large gap between top and bottom.
Re #3: Looked at objectively, there's been a big decline in the quality of the league as a league in the last 20 years. Back in the old north/south days several teams in each division began the season thinking they had a good shot at a title. Even in the first years of Red/Blue most teams seemed to have a shot at least at a title game. In the Red, Roman won in '99, O'Hara in 2000 and the Prep played Bonner, Roman, and O'Hara in championships between '01 and '03. LaSalle won in '06 and Roman in '07. But aside from the two years after Brooks left, it's been all LaSalle or SJP since then and does anyone really think that's likely to change in the next few years? Wood has been even more dominant in 3A and--with the exception of last year--WC has been dominant in 2A.
My sense--and i'd be happy to be corrected--is that in going from two divisions to three and in seeing the gap between the best team(s) in a division and the rest of the teams widen, there is less of a sense that everyone is in the same league--as there certainly used to be and as is still largely true for some of the other sports. I would be in favor of everyone playing at least one team outside their classification to make for at least four regular season league games, but I'm not sure everyone would buy that--another sign that PCL identity and solidarity are waning.
Too long a response, I know.