There are 12 matches left in La Liga this season and Sevilla are still 6 points behind it means there is still a chance, 3 of 12 Madrid matches were big matches
The determination can be seen from these 3 important matches, if Madrid manages to win 2 of them then it is certain that Madrid is the champion. On the other hand, if Madrid only win one game the competition will continue.
Given Real Madrid's previous few match then I believe the 6 points difference from Sevilla at the moment
"if Sevilla win against Real Betis today" is not completely secure. Real Madrid seems to be having a hard time winning match of late as players can't score. If you watched their match vs Rayo Vallecano yesterday, you would think it would end goalless.
Real Madrid still has a great chance of dropping points in several match until the end of this season. So I would not say they will be safe and can seal the title sooner before the end of the season if Sevilla can maintain a consistent winning streak in every match.