To be clear, this is just personal speculation.
1. In terms of lore and content
Sylvanas is the final boss of 9.1 raid. And there is no other known major villain that is worth another patch so far. It is logical to think 9.2 will possibly be SL last major patch with Jailer as final boss.
Unless Blizzard pulls some big lore twists:
- A reused Arthas/Uther/Garrosh or whatever for a content patch raid
- It turns out Jailer is good and eternal ones are bad. And Arbiter will be 9.3 boss after Jailer in 9.2
- With jailer defeated in 9.2, there will be a transition from shadowlands to azeroth or voidlords 9.3 contents patch, with non-SL raid.
But those possibilities are extremely low.
2. In terms of time
No matter when 9.1 will be released (from June to Augest), it will last probably to January 2022. From previous experience with Legion and BFA, both 7.3 and 8.3 patch lasted nearly a year.
If 9.2 is released in January 2022, and Blizzard still wants to keep 1 expansion every 2 years, which means 10.0 in late 2022, it is very unlikely that there will be a 9.3 patch.
Pure speculation
PS: “no 9.3” can be Blizzard’s best decision for SL, under the game’s current situation.
Do you think there will be 9.3 patch?