Alexandria does fall in the Walking Dead comics. It's not an immediate or straightforward collapse. A series of escalating problems, including zombie attacks and human betrayals, gradually weaken the community until it can no longer hold.
It's a complex sequence of events. The fall of Alexandria is due to a combination of factors like overrun by walkers, internal conflicts, and shortage of resources.
Alexandria doesn't have a straightforward happy ending in the comics. It undergoes a series of tumultuous events that test the resilience of the community, and the outcome is a mix of loss and survival.