Whether I can get another Reentry Permit in February 2025 for military service

I applied in August 2024 and was fingerprinted, but haven’t yet received the physical Reentry Permit document — I’d like to ask if I can get another Reentry Permit in February 2025 for military service.

If I go to Korea for military service, I’ll need to serve for 1 year and 9 months, during which I understand I can use leave to stay in the U.S. up to about 10 days once every 6 months. (I’m not sure if I can stay longer.) In that situation, since I won’t have continuously resided in the U.S. since September 2023, I’m worried my green card could be revoked or canceled during military service, making me unable to live in the U.S. — I’d like to know if that could happen. (I’d like to know if this situation could be seen as indicating I don’t intend to maintain my green card.)

Also, I’d like to know if it’s okay to complete an online community college program or an online U.S. master’s program while doing military service.