Actually, as it's a limited company, unless he's actually given personal guarantees he wouldn't be responsible for debts and assets though, as a shareholder, if the company was wound up he'd get half of any surplus. And if it was to become insolvent then there are possible actions for wrongful trading and director disqualification of course.
Anyway, leaving that aside, if it's a limited company and you own 50% of the shares then options are:
1 - Sell the shares to your partner, or an acceptable third party for an agreed price.
2 - Retain them but leave him to run the business and, presumably, keep all the profits whilst you aren't involved.
3 - It's theoretically possible, if there are funds in the company itself, for the company to buy back your shares, reducing the issued capital and meaning your partner would become 100% owner without personally having to fund it.
4 - Wind the company up and split everything 50/50 leaving him to start again for himself though if he intends to remain in the trade I can't see that being an attractive option. It's pointless.
Fundamentally, you either sell your shares or you keep them. Those are the only two options. If selling then price becomes the matter for debate. Best if you agree one. There are formulas to work out a price but nothing is set in stone and only the two of you really know what a fair price might be.