They can certainly rescind if they see you fall off. It shows laziness and lack of motivation, like you said. Dental school is undergrad ramped up on steroids.
If you cant get past that last semester at undergrad how do they know you can get through the 4 years in dental school?
I'd say buckle up and find some motivation. If the possibility of getting an acceptances taken away isn't enough to motivate you then nothing will.