Why? There's still going to be the same number of players looking for places to play. If there are players looking to play and fans willing to pay money to watch them play (or teams willing to do the needed fundraising to keep the teams afloat - hello Prince George Spruce Kings and your six-figure home annual home lottery) the leagues can continue to operate as they have been.
I'll say it again: this will re-order the hockey landscape. Junior A will revert to its prior status as a feeder league for major junior and, as a result, will likely get younger. A couple of teams may see this as the death of their raison d'etre and pack it in, but the majority are going to look for ways to adapt.
I don't know what the BCHL does, given that they have sold themselves as being the primary path from Canadian junior to NCAA, and burned a lot of bridges on the way.
But as long as there are players and paying customers (whatever the product), there will be hockey teams and leagues to house them. Predictions of the widescale death of junior A in Canada are wildly premature.
The wool parents get pulled over their eyes to pay massive Jr. A player fees may finally be taken off, but it's not like you had much of a chance of graduating from the (for example) Winnipeg Freeze and heading to NCAA under the old rules to begin with, so my gut instinct is it will probably stay the same.
For sure USports will be a loser. I think it's safe to assume the BCHL will be a loser, but they could turn it around.
For normal Jr. A teams and the major junior it's up in the air - It's just nice to be living in reality as opposed to fantasy prediction land.
I could see less interest in stuff like the Centennial Cup and World Junior A challenge, but I think local teams will be alright.
Attendance and non player-fee revenue is driven by locals playing for the team, how good the team is and how many playoff games you get to host, not if your random top line winger gets a NCAA scholarship to a below average Div. 1 school, or if the quality of play is a C+ versus a C (when compared to top tier hockey).
If teams have become completely reliant on player fees to exist, and if this ruling causes parents to stop paying those player fees, then some teams will be in trouble - Both of those things have to be true beyond what I suspect they are for it to have a big impact.