I guess it would depend on ranks and Picard's preference. If Yar and Geordi were both full lieutenants, like Geordi was in Season 2, then Yar most likely would be next in the chain of command after Data. Don't know if that would change once Geordi gets another promotion to lieutenant commander, but it seemed like he was next after Data once he got that rank and Worf went from lieutenant, j.g. to full lieutenant. Maybe the situation would be like in TOS, when we sometimes saw Sulu in command, despite the fact Scotty, as a lieutenant commander, outranks Sulu, who is a lieutenant.
Then there's the issue of Dr. Crusher. She was a full commander but never shown to be officially part of the chain of command, as her medical duties took precedence. In later seasons, it's revealed she took the bridge officer's test and serves as a watch commander on one of the off shifts, and indeed does command Enteprise in "Descent, Pt. II."
Red Ranger