Short answer: your character wont be wiped and you can continue to play with them. Focus on finishing campaign, map explored 100%, and all altars visited before participating in Season 1.

Long answer: to participate in seasonal content, you will need to create a new character. Assuming you have already completed the campaign once before, that new character has the option to skip the campaign and get right into the seasonal content. Additionally, progress you’ve made towards specifically the altars of Lilith and the map fog of war will carry over. Nothing else will, including additional renown.

Your main character will be forever playable in the “Eternal” realm, which is to say everything the game has right now. But generally people enjoy starting over every season and checking out new and fun experiences.

Reading all of these replies helped. I think I’ll try a Necro for S1, and come back to Sorc at a later time. Makes sense… but will wait until patch comes out in case they rework some classes.