Simple question, can I use the Old Base Game Yog-Sothoth with the Arkham Gates expansion and if so, if an invesitgator fails an Other World Card with a gate on it would you then just remove the gate on the corresponding Arkham Adventure card as well?

Here are the answers on the BGG thread:

https://boardgamegeek.com/thread/1530126/can-base-game-yog-sothoth-be-used-arkham-gates-exp

Essentially: Yes, you can use any of Yog's three versions; and the gate is removed and sealed .