Well, there's definitely no complete "Happy Ending" to this situation - everybody's going to lose something (the players, at least) - and the more you have invested in the game, the more you'll end up losing. There's no way around it, and since it's not possible to go back in time to correct any past mistakes, there's no use pointing fingers at Inno and saying what they should have done. Too late. The only thing they might come away with from this that might be helpful in the future - is that if there is a next time, maybe they won't crank out worlds faster than a rabbit cranks out babies.
Someone who plays in all worlds will lose 9 characters, it looks like - since they play in 11-15 as well, there would be no place for them to migrate 2-10. So that would be that much time and however much in the way of nuggets across 9 worlds - they would have essentially nothing to show for. Granted, a computer game is always like that - once you're done, there is nothing concrete to show for the time you invested. If you completed the game, you can have that satisfaction knowing you finished it - but in an ongoing game such as this, there's no 'finish' for you to reach. You just play until you're tired of playing, and then you just leave off. It isn't easy, since you have that guy on the screen with all that gear and all those EXP and Health points you worked so hard to get - but those are, after all, just numbers on a screen. To throw them away seems like such a waste, but what do you stand to gain by not deleting them? if you're no longer having fun - if for some reason the enjoyment you used to get from a game is just no longer there - what point is there to keep playing? All you get is frustration and aggravation, and certainly no more enjoyment - so there's no point to keep playing if the game is no longer enjoyable.
The fact of the matter seems to be that player characters on certain worlds will either be migrated to other worlds or eventually deleted along with the world. No consideration can be made for the preference of individuals for keeping one world over another - and by now it's clear that there is no way to inject more life into the older worlds, so they're eventually doomed. Towns, alliances, forts - everything you're familiar with on world 2, for example - will be scattered to the newer worlds somehow, but not in full. If you're part of an alliance in w2 with 75 forts available to them, there's no guarantee there will even be such an alliance in your new world, let alone that you will be a member of it. And will all the same people be in your new town, your new alliance, your new world? Maybe, but again maybe not. That can't be predicted yet until they know how characters will be moved. But don't count on anything like the situation your character is in now - there's no way it can possibly be the same on another world where things have been established for a long time already. You will be the newcomers and you will have to find a place for yourself. If you still have, or can come up with, enough enthusiasm to essentially start over again, you can build a town or an alliance that can bring change to your new world, but it's going to take considerable effort, which a lot of old-timers may no longer have. You spend 3 or more years in the same town or alliance with the same friends, it gets pretty hard to change things - especially if the change isn't your own doing, but is being forced on you. That's where many older players will drop off. Their comfort level will just vanish when they are moved, and many of them will vanish themselves once that happens.
So there's no point in arguing for keeping the older worlds - the best you can hope for is that you get used to the idea and when the time comes, that you can adjust yourself to your new world(s). If you can't, sadly the only other option is to stop playing. But seriously, you weren't planning on playing this game for the next 10 years, were you? Eventually you were going to end up dropping it. It's just that that day could get here sooner than you had expected.