Imagine followed by??

I think imagine can only be followed by "that"

So is this wrong

Can you imagine if he had done that?

or should there be another clause

Can you imagine (what would've happened) if he had done that?

Can you use the present with "imagine" or only the past as it's usually used in a conditional clause replacing if?

Imagine the company starts making fewer sales, they'll go bankrupt.

Thank you so much