I think, i heard, it is not a bad break of a vow. Means you don't reach hell for it. You are free to leave, but try not to talk bad about your teachers and about the mahayana - that is the only dangerous thing, to be contemptuous in speech.
The calculation is very simple: if you do the practice you will find a binding (samaya) to the teaching and to the teacher. If you don't, you will stay away from it. Nothing else happens.
Because, if our mothers, who have been kind to us
From beginningless time, are suffering,
What can we do with (just) our own happiness?
From 10th of 37 Bodhisattva Practices