They could just do re-issue events and/or perma re-issue events like FKG does. Those don't hurt old players, nor they hurt whales. They actually help all players including whales to get content they missed, and having just re-issues on the side of main events doesn't hurt whales who got everything before. As long as you don't think letting new people get old content hurts old players cause the had stuff you don't just cause they got into game faster.

Hek - it could actually bring more revenue for devs. We have so much events, that F2P cant really spin 900 kobans pachinko for girl each event, add the fact that there is more than 1 girl and that you need luck to get event girls (if you didn't farm all troll normal girls before-hand), and you end up with situation where its actually harder for F2P people to get premium content girls, which could force more of them to go whales and buy kobans to spin more times. Just having re-issue events side-to-side with normal events could force some "stamina" refilling for having more chances to get event girls from trolls (for new people mostly).

Thats just my idea of solving this "old content not available anymore" problem. Thou personally I find HH premium content to be to damn expensive for me to even care about it, but it would let me get F2P stuff I possibly missed.