so I was wondering... after u bet irencius can u still play the game or do u have to start a new game to be abel to play the ToB part?

From SoA to ToB spoiler
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if you play SoA with ToB installed, the end doesn't break = after the final cinema of SoA, you immediately get to the opening cinema of ToB and then to the game itself.

if you install ToB after you finsihed SoA, there are basically three options:

1. start a new game,
2. import a SoA save game to start ToB,
or, I recommend,
3. play the SoA final battle (if you have a save game there) again, and make the game pass into ToB; this way, you'll get the XP for killing irencius and his goons.

And, more importantly

SPOILERS
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The special abilities from the Tears of Bhaal!

Ya as long as you have ToB installed then your party gets teleported to ToB starting area once you have killed Joneleth in Hell.