General Advice needed: Return of Palpatine event?

I'd keep with your droids if that's your arena team. I doubt the Emperor event will be back for at least a couple more months. Even if it does, it runs for a week, so you'll have time to finish off those last couple rebels.

As for the Yoda event, it doesn't come out of nowhere. It's monthly (2nd Thursday of each month I think) and there's a countdown on it in the events section when it's not live too, so it shouldn't be a surprise. Hope that helps :)