Not a maxis user here, but i travel a lot with traveler sim too. To answer your question:
1. If active roaming for traveler sim, it WILL NOT auto activate for maxis.
2. Roaming is only for data usage. As long as your line is still active and connected to the local telco there, you can still receive call and sms. However, it will be costly.

Remember, if you have dual sim, always activate roaming for traveler sim, then turn off roaming for main Maxis line. With this, you will not be charged for using mobile data over there.