Why is Marshall not on How I Met Your Mother season 9?

Segel was the only one who had opposed season 9 of HIMYM as he wanted to concentrate on other work. It was the Himym producers that convinced him that ending the series in season 8 would be too abrupt. So they might have given him a concession by a separate shoot at his convenience.

Will there be a season 10 of how I met your mother?

According to E! News, Bays told Reddit that a season-one cancellation would have resulted in them writing Victoria in as the mother. Of course, the show actually went on for nine seasons, so that plan got scrapped.

How many episodes are on season 9 of how I met your mother?

24 How I Met Your Mother - Season 9/Number of episodes