MaccyH, That's really nice of you, but I (I realise others don't agree) don't see why YOU should pay your DH's maintenace payments. Why should you work harder, see your DCs less, have less quality time with DH, so that DH's exW doesn't have to do those things?
I don't think either that you/he should stop paying (just to be clear), but if it were me I would fully expect to reduce the monthly amount paid.
Also, just to be clear, if my exH started to earn less, I would fully expect him to reduce his maintenance payments for our DCs. In fact that did happen. Of course I would expect him to...why wouldn't I?..absolutely no question. Yes, it would make life more difficult for me, and yes I'd have to work harder, and yes our DCs might have to go without some things. But that is life. If we were together and his income dropped, all those things would still be true.
I wouldn't see why exH's DW and her DCs' standard of living should be even further reduced so that I didn't have to alter mine.
That said, I would expect to be given notice of the drop in maintenance to enable to me to be prepared for it, and to make adjustments. And if your DH's exW might react badly, this would also give her time to adjust emotionally to the idea.
In addition, if your financial stability is likely to be poor for some time, she might be better off taking a drop in maintenance but be able to expect it to continue at that rate, than to suddenly find you and DH are in really dire straights and she's all of a sudden getting a fiver a month.