Because he left the country before his H-1 extension petition is

his such petition is regarded abandoned.

If his last entry was under H-1, he will receive an I-94 with same number. There is no such thing that an I-94 becomes invalid because of its number being used/submitted.

He can not renew/extend his I-94.

When he goes to Canada, that would be a good chance for him to apply a new H-1 visa using his H-1 extension approval notice.

In case his H-1 extension approval notice is available to him before he enters US, he may try to use it at the customs. When CBP officer makes a mistake, I-94 may be stamped a longer stay period.