It's gonna be something they're gonna have to think carefully about. Maybe don't allow them to begin and if the game is a success put in the time to figure out.
My suggestion is the renter should have to pay to revive them (with the potions) when they're returned and still in cooldown.
My current thought - and keep in mind this is just a thought - is that we make it so that only season rentals can be used in Survival Mode battles, and then we make it so that all cards come off cooldown automatically at the end of each season.
lots of renting those last couple days of the season. But then again how many will be left end of season would be interesting (may not be very many) may even out. But yes... i can see how that could work and not be too much work.
Yep - it's very hard to predict exactly how this will all play out. Which is also pretty exciting in my opinion. I expect it might take many months before players arrive at optimal strategies.