I would imagine so. means. Yes, probably so. Yes, I think so. It's a polite, reserved answer.

Would Imagine meaning?

used for saying that you think or hope that something is true, although you are not certain. I would imagine she's at work. I'd have thought they'd be grateful for your help.

How do you use imagine?

From Longman Dictionary of Contemporary English I would think/imagine/sayspoken used to give your opinion about something when you are not very sure about it I would think you'd be happier in a different school. 'Will it cost a lot? ' 'I would imagine so.