Re: Can calendar events be activated again after deactivating them by mistake?
Yes @SimTecnologic you can recreate them yourself. I do this regularly, I'll attach some info for you.
I regularly delete Harvestfest and Winterfest for example and then add them again.
But, actually some of mine return automatically despite being deleted several times so you could also complete the Sim calendar cycle and they may return on their own. Things like Neighbourhood Brawl, Night on the Town, Rebate Day, Lottery, Skill Day, Talk like a Pirate Day all come back automatically for me. You could wait and see if yours do the same and if not just add them back. To speed it up you could shorten the seasons to 14 days but shortening to 7 days might skip over some.