my entire Story Progress is gone. I even got the AV that I killed Malthael but I cant start the Adventure mode.
If you delete or Rebirth the non-Season Character that completed Campaign Mode, your Progression gets reset. I learned this the hard way a few years ago.
Now, I have a “placeholder” non-Season Character that has completed Campaign Mode (Normal and Hardcore) that I never delete or Rebirth. And, I have a main Character (Normal and Hardcore) that I Rebirth every Season.
Since I play Seasons on all 3 Regions, I’ve done this on Americas, Europe and Asia Regions.
Between Seasons, I strip my mains, to get them ready for the next Rebirth. I pass the time by playing my “placeholder” Characters in non-Season until the new Season starts.
Good luck and good hunting! 
Asᴋ ɴᴏᴛ ᴡʜᴀᴛ ʏᴏᴜʀ ɢʀᴏᴜᴘ ᴄᴀɴ ᴅᴏ ꜰᴏʀ ʏᴏᴜ
- ᴀsᴋ ᴡʜᴀᴛ ʏᴏᴜ ᴄᴀɴ ᴅᴏ ꜰᴏʀ ʏᴏᴜʀ ɢʀᴏᴜᴘ
I do not hide from my enemies.
I do not run from my foes.
I seek them out; I hunt them down;
and then they’re quickly disposed.
~ 𝑃𝑒𝑟𝑢𝑠𝑜𝑒
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So I have to clear the Story again ? I mean, I never deleted my “Main” I played most time on when seasons werent even a thing back then 
If non-Season Adventure Mode is locked for you then, yes.
If you have a friend that has completed non-Season Campaign you can get them to start a game in Act V for the last Quest. Have them invite you and both of you kill Malthael. That’s the easiest, quickest way to unlock non-Season Adventure Mode. And it can be done on Normal Difficulty.
You could also ask someone in Chat to help you get the Malthael Quest.
Note: In Seasons, Adventure Mode is always unlocked. But, it does not carry over to non-Season when the Season ends. (That’s why I keep “placeholder” Characters that have completed Campaign Mode in non-Season).
Personally, I wish Blizzard would have a permanent global flag (or Achievement) that marks Campaign Mode completion and prevents Progression reset in non-Season. As it is, it’s a waste of 2 Character Slots (Normal and Hardcore) per Region.