I'd be interested to see what the other experts think but my thinking is as follows:
He can use the money to do what he likes but this will dramatically increase your share of equity in the property - depending on your terms this might cause you an issue at a later date - you will need to check the wording of your T&Cs regarding the equity point as creditors may want an amount equivalent to your share of equity.
Also, if the property is then mortgage free you may be able to 'remortgage' at the relevant time, if this is also one of your terms. i.e at month 54 your share of equity will now be substantial so creditors might not accept a simple '12 month extension' equal to your monthly contributions. However they may not have a choice depending on how your t&cs are worded - again you may be forced to remortgage, which despite the normal credit rating issues might actually be possible if the property is then unencumbered and you are seeking a secured loan.
Perhaps your husband could use some of the money to help you with a full and final offer instead?
If accepted your IVA should be closed earlier and you are free to do what you like with the property...?
Video here on F&Fs:
https://youtu.be/h4dozq9aGak
