Restore HP for Raid Battles - Clarification
I see many people asking about "chipping away" HP of Raid boss so I'd like to offer an answer about that based on what I've read from the game's own website.
https://support.pokemongo.nianticlabs.com/hc/en-us/articles/115009004747-Raid-Battles
"At any time during the battle, you can flee to heal your Pokemon using potions or revives and then rejoin the battle."
So, based on that statement, you CAN chip away Raid boss HP as long as you flee before you last mon faints. Then you quickly revive, restore them or pick another 6 mons to battle the Raid boss (now with reduced HP) again. Only thing you need to watch out is the time.
Answers
If no one is inside the raid and you are solo are you sure that you can leave, enter again and the raid boss will be at the same HP?
Because I was pretty sure that his HP resets when no one is inside the battle on the group that you enter at the beggining and as soon as you leave you have to create another new group resulting on the raid boss fully recovering.