I think it would be better to dissolve 343 move the remaining 343 employees to other MS, Bethesda and Activision Blizzard studios.
Then I'd let ID software lead the new Halo game at the same tine they work in the next Doom, with support from several teams from Microsoft (Infinity Ward, Treyarch, The Coalition, Machine Games, Blizzard who would help them sharing their best expertise in shooters gameplay and design, MP, GaaS, art or visual tech). The idea would be to rebuild Halo being true to its roots and core pilars but modernizing and refreshing everything else getting stuff from the other games that works today.
Hiring after significant layoffs... I don't understand this management style at all. Couldn't you just have at least the team let go work on some expansion packs or have another game be in early development to have them move on to so you could avoid this?
The idea is to fire less productive people, people whose output has less quality, people who maybe are burned out or who has a too high salary for to the job they do. And then hire people with fresh energy, expertise, knowledge and potential in areas where they need to improve.
One of the reasons of firing them was that they weren't capable of including what they had at launch even if they had the game delayed a lot, and because a good amount of time after release they haven't been able to release a meaningful post launch output.
So they may be trying to replace some people to see if they can fix this.