Maybe.
I'm not quite sure why you would have your watch in airplane mode while your phone in not in airplane mode? Maybe, for what you want, try putting the watch in Do Not Disturb mode or Silent mode and the notifications will be there when you are ready to look at them.
Regardless, the way it currently works is, at the time the notification first arrives the phone has to work out where you are most likely to see the notification. If it can't locate the watch because it's off or in airplane mode, it won't send it to the watch.
I suppose you could send feedback to Apple to suggest/request that your unread notifications could keep trying to find you until they are seen. Reverse example, you could request that if the watch has unread notifications and the watch is turned off or to airplane mode that all those notifications transfer back to the iPhone to be read there.