If rebooting the phone doesn't work you could try going into Settings then look for emoji keyboard and check it's switched on. Hope you can get your emojis back. Phone issues can be so frustrating. Good luck.
I know this may sound really silly but can I just ask, have you tried switching it off for five minutes then switching it on again? Itβs a bit like the βhave you switched it on at the plugβ question but the odd occasion mine goes strange this seems to sort it.