Two part post
1. Are you certain that the total amount secured on the house as joint debts (the mortgage and any other charges you know to be joint) equals or exceeds the value of the house? If it does, then:
a) Voluntary repossession may be the best course of action if neither you nor the executor can afford to get probate and sell the house yourself. However, it is generally the case that repossessed houses sell for less than others and the mortgage lenders often seem to find a hell of a lot of fees etc. to add to the costs; and
b) Any shortfall in the joint secured debts (i.e. money owed to the lender(s) after the sale because the sale did not raise sufficient funds to cover all the costs) would be your reponsibility.
2. If there is still equity in the house after the joint debts have been cleared (i.e. the sale proceeds would exceed the full amount of the joint secured debts) then you are entitled to half that equity. If you go for voluntary repossession in this situation you need to accept that your share of the equity will possibly be reduced - because of the extra costs in 1 a) above - as compared with selling yourself (assuming you could get probate and sell quickly before too much mortgage arrears built up). Also, you have to be very careful that your share of the equity does not get used up to pay off any secured charges which were entered into by your ex in his sole name.
3. In the situation in 2 above, it is a judgement only you & the executor can make as to whether to allow repossession. I assume there is not much (if any) equity. If so your share of what there is could easily be used by mortgage arrears, court costs, probate & selling costs so the repossession route may well be the best. Obviously, this would not be the case if there was a lot of equity.