I *think* as long as together you still meet the financial requirements and can explain any time apart it should be OK, but I admittedly don't know where that would be in the official guidelines so I hope the experts see this. When applying for citizenship there is a limit for time outside the UK, and you must be in the UK on the date 3 years before you apply.
Also, i hope your husband is OK. Lots of support to him and his mother as she (hopefully) recovers! So sorry he has to head back on such short notice.