revising of four sentences

[vil]

Dear teachers,

Would you been kind enough to share with me your opinion concerning the following sentences?

He couldn’t leave.
He wasn’t allowed to leave.
He was not to leave.
He shouldn’t have left.

Thanks for your efforts.

Regards,

V.

[Tdol]

What exactly are you after? Obviously, they're all fine as sentences, the second is more restrictive than the first and the reason for his not leaving is external, the third could be part of a narrative, etc.