When you go to do it finally, you still have to pay for the time it wasn't renewed.
I know the website says it's all good to be running around with an expired sticker right now, but I went and got the one I needed because I know people that still got tickets for not having it AFTER April of this year, so the MTO can say all they want, but you can still go to the office and renew and the coppers will do what they want anyway. I'd rather not give them a reason to write a ticket.