In a somewhat recent past, they bonded cadets for 7 years. You can still leave, but they will try to take an amount of money from you depending on your years of service.
Don't count on bases to reopen anytime soon. If they do, it will be due to extreme pressures from industry forces.
If you join as a cadet, you will start as a Second Officer. Even if they miraculously open the basis, they will unlikely give you a base at that rank. There is a high chance you may never upgrade.