Midway without USS Yorktown

What if USS Yorktown could not reach the Battle of Midway?

The US Navy would still attempt the battle with two carriers, with some benefit from concentration but substantially less capability.

The US Navy had already planned to fight with two carriers if Yorktown could not be repaired in time. Her absence would therefore leave the operation going ahead with the smaller force. That could help concentrate the remaining carriers, but it would remove a substantial share of American capability. There is no confident prediction that the battle would go as well without her.