Every Flash fan out there as seen and heartbroken that Barry Allen AKA The Flash has sacrificed himself for saving the city from speed force leak/attack.
Speed Force was leaking energy all throughout the city because it needed a speedster to be prisoned sort of which was Savitar at First then Jay Garrick sacrificed himself in order to save Barry Allen and Wally West, but during the last episode of season 3 fight cisco made some changes in the cannon bazooka to get Jay Garrick out of it.
And at the end of the episode speed force comes to Barry Allen (The Flash) in form of her mother, asking him to surrender in order to save the city and We saw the heartbreaking moment of Barry Allen going into the speed force for good.
Season 4 Villon is not a Speedster:
Okay so we know from the news updates that we get from Team Flash on CW that season 4 will be different as all three season they had a speedster as a Villon i.e. Season 1 -> Reverse Flash, Season 2 -> Zoom, Season 3 -> Savitar.
Season 4 Continuance:
We have also seen season 2 was based on the ending of season 1 when worm hole was opened and we get The Zoom & season 3 was connected with season 2 ending when Barry Allen AKA The Flash created a Time Remnant in order to defeat Zoom and we get Savitar for Season 3. Now as we know season 3 was finished where speed force was leaking all over the city, So, we get a lot of meta action on Season 4 for sure.
Wally Saving the Day:
As Barry Allen is gone Wally West will be taking over his place for a while, We even might see Wally West in Red Flash Suit for may be a couple of episodes.
The Flash Rebirth:
Okay so we know Barry Allen is gone into the speed force and he will be back within the couple of episodes for sure as Grant Gustin paying Barry Allen has signed up for at least 7 Seasons with CW for The Flash. And According to comic book The Flash Rebirth Would be coming to season 4.