handling prepared strikes

Whats a decent way to handle when an entire party prepares a nova strike?

This comes up a lot in Tier 2 and higher. Hypnotic pattern happens. banished things return. Also ambush situations, even in Tier 1.

I think this is a decent take on it:

Initiative is already rolled and technically still running, so depending on time and how much of a fight is left, you can continue using the established sequence, ask for a complete re-roll, or simply re-roll for the returning combatant/s.

The entire team who is striking (be it PCs or NPCs) declares reactions to use a single strike (like opportunity attacks. You don’t get full actions.)

If tricky stuff is involved like “teleport when damaged” or “contingency whatever” or “shield spell blocks the hit” or “grant disadvantage to the attack” then timing of reactions comes into play. Based on the resolution of reactions, the first strike would hit on the person’s initiative, then the target wakes up (automatic reaction effects like “teleport when damaged” occur but not usually pre-active reactions (my word for such things as Shield, grant disadv to the attack-- things that involve choices before the action) because they can’t use pre-active reactions when held/incapacitated/etc until after they’re woken…), then all the other reaction-based strikes occur, then enter initiative sequence normally. The only area open to excessive abuse is players knowing the initiative sequence and timing it precisely, which is a big reason I’d consider re-rolling the returning combatant initiative. So:

1. Single strike from person X, which can trigger an automatic reaction from target if available.
2. All other single strikes, one of which can trigger a pre-active reaction from target if available.
3. The rest of the turn of person X. (They used their reaction to get an extra strike on their turn.)
4. Whoever is next in initiative order, and continuing in initiative sequence like normal.

Other situations:

That’s assuming the party wants to attack “after Johnny’s hit on the beast”. If instead the party gets clever and wants to attack “when Johnny’s about to hit the beast” then one of their attacks (whoever is first in initiative makes sense) wakes the combatant which then has a greater chance to go on this round. /shrug it evens out.

What about not-surprising strikes, like when you're negotiating and they see you clearly but some ass next to you steps up and sticks a knife in someone’s face? There’s no surprise on either side, even if you’re talking friendly and it’s not expected. Just roll initiative. The initiator uses their declared action (or changes it depending on conditions) on their turn. Everyone else sees the shot coming, or saw it happen, and acts as normal upon their turn. Draw weapon and attack, move, whatever else.

What about surprising strikes, like when you're negotiating and they see you clearly but some *hidden* ass in the back decides to launch an arrow? (keyword, “hidden”, meaning ANYONE with passive percep under their hide score does not know where they are and will be surprised.) Still roll initiative. Anyone not surprised takes their actions on their turn just like a non-surprising strike, because “WTF everyone else, didn’t you see that coming a mile away?” Anyone surprised can’t take actions until next round. The initiator uses their declared action (or changes it) on their turn, in initiative order like normal.