If units tie in combat, do they exhaust back?

No, units do not exhaust when recalled due to a tie in combat.

According to RiftJudge FAQ #7084, recalls do not change the state of a permanent unless specified; the unit maintains its current ready or exhausted state. Furthermore, RiftJudge FAQ #3001 clarifies that a unit only recalls exhausted if the effect specifically states to "recall exhausted."

When combat ends in a tie (both players have units remaining at the battlefield):

1. Combat Cleanup occurs.
2. All units are healed.
3. The attacking units are recalled to their controller's base.
4. The units retain their ready/exhausted status from before the recall.

If a unit was exhausted before the combat, it remains exhausted upon being recalled to the base. If it was ready, it remains ready.