Bonus

A bonus is just that, a bonus. That is in no way shape or form part of your wages unless you have a contract that says it is. Since you didn't mention a contract then no, do not ask about it.

"Lose nothing by asking" Yes, actually you do. If you want to be the employee completely out of touch with potential struggles in the company, if you want to scream, it is about me, then ask.

Think about it this way, every year you give your kids amazing birthday presents. You have a hard year so you spend a fourth of what you normally do. You want so badly to give your kids everything you did in the past but you can't! Then your child comes up to you and asks where the rest of their gifts are. Got that feeling kicking around in your mind, that is exactly how you would make your boss feel if you ask. Okay maybe not exactly but damn close.

You can forgive your kids but bosses are not prone to letting those feelings go.

No don't ask. That ride may be over.

A bonus is just that... "bonus" and something you cannot and should not count on.

I am sure much of it depends on the stability and financial situation of the company your work as well as the economics of your area.

ETA: You've changed your post. You stated originally your husband, NOT your employer. I agree with Julie S. A bonus is just that a bonus. Had the post originally stated EMPLOYER not husband, I would have said the same thing that Julie said.
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What? Your husband takes off for four months and leaves you and the family???? HUH????

If he typically gives you a bonus for accepting his leaving for 4 months, ask about it...

this just sounds freakish to me...sorry.

Nope.
Might be the new normal.

While I can understand your hesitation to ask for a bonus (it's a bit like asking for a gift), I think you probably should bring it up. You can explain to him that it's a change from the past and you are wondering if it means he is sending a message about the quality of your work or if there is another reason. Maybe the company is in major financial trouble or he just forgot. In any case, it seems reasonable to ask why (politely).

I'd ask. You lose nothing by asking.