The likely scenario is that, immediately upon Parliament resuming next month, the Liberals will immediately lose a confidence vote, triggering a snap election. The opposition parties have all stated that they will initiate a confidence vote at the earliest opportunity.
In the unlikely event that doesn't happen, I imagine JT would remain on as PM until the mandatory election this fall. Were he to step down, he would probably appoint a sitting MP as interim PM.
As a fun(?) aside, Canada has had two PMs who served while members of the (unelected) Senate, and MacKenzie King and John Turner both briefly governed without a ministerial seat.
Okay then, the next election will happen when the next election is called.
Let me know if I used any words that are too big for you.