I think the best way to deal with the uncertainty about his visit abroad and how it might affect his grant of citizenship is to phone or email the DIA and ask the various questions. I've seen on the threads that during lockdown, when certificates of citizenship were being mailed out (when the ceremonies hadn't yet been resumed), DIA delayed printing one person's certificate until he would be back in the country, exactly so as to avoid causing problems by invalidating the visa he was travelling on before he got home. If they could do that, it looks at least possible to me that they might agree to keep your husband's PR visa active and schedule him for a later citizenship ceremony. This strikes me as one of those times when it's got to be worth asking the authorities about YOUR OWN case, rather than worrying and trying to guess.