For the betterment of Atletico Madrid, Semione should be replaced with young manager with good coaching skills.
Considering how long he manages Atletico Madrid, some of their systems should be designed around Simeone so replacing him would take time. I wonder if the fans want that though. By fans, I mean those who travel and buy tickets to watch them play, not social media darlings who speak about "we are in a crisis" whenever their favorite team loses. Most of the time they're farming for views with their terrible analysis of a match. Aiming for trophies is a good thing, especially if it's a CL trophy. The question is whether replacing a coach will magically answer that or not (probably not).
If we are talking about Atletico Madrid's chance to win a Champions League title, then I don't think it will happen in the near future. 
While Real Madrid is getting Mbappe and there is a Manchester City fact too, it is really not easy to reach the title. Besides Atletico Madrid's lowest expectation in this tournament isn't winning the title. Even a quarter finals qualification is seen as good achievement.
The board are really contented with the way Simeone is managing the team. They even extended his contract not much time ago. Would he like to achieve a Champions League title? Who wouldn't?
But Atletico Madrid need to make a huge improvement to reach even the finale once again (The last time they did it was the 2015/2016 season).
While Real Madrid is getting Mbappe and there is a Manchester City fact too, it is really not easy to reach the title. Besides Atletico Madrid's lowest expectation in this tournament isn't winning the title. Even a quarter finals qualification is seen as good achievement.The board are really contented with the way Simeone is managing the team. They even extended his contract not much time ago. Would he like to achieve a Champions League title? Who wouldn't?
But Atletico Madrid need to make a huge improvement to reach even the finale once again (The last time they did it was the 2015/2016 season).Atletico madrid is still on their capacity to "exist", not on "win" the champion league. Diego simeone, as atletico madrid's coach never had a great expectation for his club in UCL; therefore, even though they were not favorite to do this, atletico madrid still has little opportunity to win UCL.
Although the officials of Atletico madrid were always improving their teams, their efforts were pointless since the gamplay and strategy of the simeone remain the same. When atletico madrid advanced to any level in the champion league, such quarter or semi finals, ATM officials feel good enough.
With the present team, Atletico Madrid lacks capacity to win the UCL. Atletico madrid made it to final at 15/16, really lucky. So in essence, all things considered, it makes little difference how much atletico madrid improves; uninspiring strategy and gameplay by Simeone will prevent them from winning UCL.