This is probably more of a partnership law question than an intellectual property matter. The trademark would be just another piece of partnership property, to be allocated, or liquidated and allocated, according to the statutory rules (and/or the partnership agreement terms) upon wind-up of the partnership's affairs.
By the way, winding up of a partnership's affairs follows, not precedes, its dissolution. When a partnership dissolves, it should cease to engage in new business (unless a subset of the former partners elect to carry on the business), and must begin the process of paying creditors, liquidating assets, collecting receivables, and otherwise shutting down.
If all partnership property has been disposed of except for the TM, all bills paid, and each partner has received his or her share of the remaining money (or other assets), the wind-up and liquidation process is incomplete, and more likely than not, the former partner is entitled to receive half of the TM's value. It's sort of like in a divorce, after the final decree, and the newly-single couple is cleaning out the attic and discover a pile of shares of Intel stock they forgot they had. Let's see, did the property settlement say SHE gets all the stock? Or did it explicitly divvy up the portfolio except for the forgotten Intel?
You might want to look up Corporations Code sections 16401 and 16402 regarding partnership property and 16801 to 16807 regarding winding up a partnership's affairs. Also consult any written or for that matter oral partnership agreement or modification thereto that might alter either partner's rights to the TM.
