Buildersmate's answer is spot on.
If it's a partnership it needs leagally dissolved and there will be issues over who can continue to use the business trading name and such-like. It needs legal and professional advice.
If it's a company, and your husband is a director (which he would normally be with 50% of the shares but doesn't actually have to be) then he can't just be "sacked". It would require a vote at a board meeting. If there are only the two directors then unless he votes to sack himself he can't be sacked. If there are other directors then in theory he could be sacked if the right hoops are jumped through. Likewise, if he isn't actually a director then he could be sacked.
However, he's still a 50% shareholder so he could apply to have the company wound up and the same issues would arise as with partnership. Again, detailed legal advice required.
Certainly the other guy can't just tell him "you aren't coming back" and forget about it. Nor can he pay himself a dividend on shares without paying it to ALL shareholders (although he could get round that by paying out profits to himself as salary rather than dividend).