Is it grammatical to introduce a result clause using “then”?

Is it grammatical to introduce a result clause by using then as in these examples:

• Don’t be lazy – then you will fail.

• Don’t kill him – then you will regret it.

If so, then is the then in these examples a conjunction?

I’ve not found any resources that mention this – they usually say that result clauses are usually introduced by conjunctions such as so or so that which in the above examples would read:

• Don’t be lazy so that you then fail.

• Don’t kill him so you regret it.

Idiomatically, the better word or phrase for those examples is "or" or "or else". I am not sure about the technical grammar of them.

"Don't be lazy or you will fail."

"Don't kill him or else you will regret it."

Your examples seem fundamentally flawed, in that the clause then you will fail could logically refer either to [If] you are lazy or to [If] you are not lazy.

Work hard, then you will succeed would seem to be a better example, (and unobjectionable); but are you asking specifically about negative exhortations?