Random encounters has been proposed, but ultimately I think it would just bog the game down and not really solve all the issues with Long Rest and the fact that the story has already put time limits on things.

In telling you, the only solution is to implement some sort of timed events that explain why the druids don't finish the ritual, and why the goblins don't attack not matter how many long rests you use. It least if the do timed events triggered by too many long rests, they can explain why these things havent happened and provide some additional side quests and such for "taking too long". Side quest complications would make it more interesting and fun.

But if you do this, you gotta reward players still for NOT spamming long rests. In this way both are rewarded, just in different ways.