We have been using Adobe Mobile SDK to track our apps. my question is, let's say if we plan to move away from Adobe and decided to use other analytics tool to track mobile apps.in that case, do we have to remove the mobile SDK on the App code? or will there be any strange error/messages if we just keep the Adobe Mobile SDK and not use Adobe anymore?
If you decide not to use Adobe SDK, I suggest you to remove it from Application Code.
But if you are in dilamo or have a plan to turn it on later, you can still keep it in your Application Code and ask developer to turn off the settings related to Adobe SDK so that you wont have issues with Server Calls (Make sure that Server Calls are not firing while you turn off the settings related to Adobe Analytics). Later, you can turn on the settings without SDK push to the customers.
You could leave it. The only thing I would guess is down the road your dev team may like to keep the app as lean as possible from a size and code base perspective. Also down the road if its left compatibility issues could creep in as OSs and other app sdks evolve. Remember if you abandon it, your app (unless the RSID is removed) will send data and use server calls to Adobe backends regardless.