by FAR the BIGGESt key to a successful keeper league is to have a strong core of owners that stick around. My league has been either 10 or 12 teams for about 9 years. 8 of the original 10 owners are still playing and all 12 have been around for the last 3 years. Occasionally we have to replace one here or there but as long as you have a strong committed core your in good shape. There are a few different ways to do it when you have a team or teams leave the league. 1)If it is just one team leaving, you have the new owner just take over the old owners team, name his keepers and go from there. If you have more than one you can either a)flip a coin and 'assign' an old team to a new owner. Or throw all the players from departed owners into a pool and have the 1,2 or more new owners take turns 'drafting' players from that pool until they reach the number of reserves needed. Another possibility, is in auction leagues you can just not let the new owners reserve anyone at all and basically they have the entire salary cap to work with. In other words they have more money.
"THERE WAS SHRINKAGE!!!!!" - George costanza