I would argue that being able to miss out on the crypt or certain companions, etc. is one of the great features of this game.
I'm on my 7th playthrough and still have not got the owlbear cub in my camp. I didn't discover the kua-toa until my 3rd or 4th playthrough. You could miss the hag, the harpies, or even the entire underdark. It gives the feeling of reward for exploration. And even if you are thorough in your exploration you will have to wait until subsequent playthroughs to experience everything.
Anyways, he could always go to the crypt much later in his playthrough. There is luckily no required order other than some content being too difficult for 1st-3rd lvl.
