I see no point in talking about which riders may leave if there is one big league, as they may leave anyway as many have, you can’t stop them.
You have to build the product with what is viable and what is available, I think I say it every season, the biggest issue the sport has is running costs, bikes cost to much to buy and run, promoters then have to pay a fortune to them and fans pay the promoters back but everyone except the riders and tuners are losing money.
One league or three won’t make any difference until costs are brought under control.
At some point the sport in this country is going to have to take more steps back before it can go forward, and I am talking semi pro at best, so National League late 80s but without nine and ten point calibre riders of that time, or the team version of grass track and lots of people go and watch that without big star names.
You would have to go smaller size teams until enough new riders can be trained and again that’s where runnings costs comes in plus you would need a proper training program.
They had the same issue after the War, different times but the problem is the same, not enough riders.