If you hide a Zhonyas but decide to flip it later to no death, can you do that and it'll go back to base as a normal Zhonyas?

Yes, you can do that. You can reveal (flip) a hidden Zhonya's Hourglass at any time you have priority to play a reaction, even if no unit is currently dying.

According to RiftJudge FAQ #1981 and #1959:

• Gear cannot exist at battlefields. When Zhonya's Hourglass is unhidden/played from a battlefield, it immediately recalls to your base.
• You can reveal and play a hidden Zhonya's at any time you can use a reaction, not just in response to a unit dying.

Sequence:

1. You have priority (e.g., during an open state on your turn, or in response to a chain item).
2. You reveal the hidden Zhonya's Hourglass.
3. Because it is Gear and cannot exist at a battlefield, it is immediately recalled to your base.

Important Nuances:

• Timing: You cannot reveal a card on the same turn you hid it (standard hidden rules).
• Priority: On your turn, you can do this at any time you have priority. On your opponent's turn, you must wait for a chain or showdown to have the priority required to play a reaction.
• No Death Required: You do not need a unit to be dying to trigger this; the act of revealing it is sufficient to send it back to your base.