There are a couple of options with Shared Parental Pay (ShPP), they aren't necessarily great, but just to put it out there:
Option 1: He could stay at home and look after the baby and you could return to work. This could be just until he is fit and then you go back to looking after the baby and he returns.
Option 2: You could both take Shared Parental Pay at the same time until he is able to return to work, this would bring your total maternity/ShPP forward. However, if he qualifies for ShPP then he probably also qualifies for Statutory Sick Pay, and he can't have both, so you may be giving up SSP to get ShPP which is a bit more, but uses up weeks of parental leave that you could otherwise have taken.
Both of these options would require both of you to meet the qualifying criteria for ShPP:
Be employed continuously by the same employer for at least 26 weeks by the end of the 15th week before the due date
and
Earn on average at least £118 a week in the Relevant Period (approx weeks 24-15 before due date).
(assuming you want to take some leave as well as him)
(being signed off sick is still employed by the way)
You might also get slightly more income than you think as you might be due a income tax refund when you go on maternity/ShPP - exactly if, how and when this turns up is pretty complicated.
He could also be due one if he is on PAYE and has gone from earning a lot to earning not much.
There is a after tax/take home maternity pay calculator here:
www.maternity.money which will give you an indication although you should always double check with your HR team.
Hope this helps