the way inactivity system currently works is that a team gets marked inactive when all the player contracts run out. I do not have a better solution for this right now. Maybe in the future we could do a vacation mode where you can enable it for certain amount of weeks and your team and it's contracts just get frozen.
Right now I'd recommend reseting the team in this case, but change the team name first if you want to use the same name. Another possibility is to just get new players from market/scout/academy, but the decision is up to you.
Thank you for your interest in the game!