system
Given the following post, respond as if you're commenting on Reddit:
human
[Portal] GLaDOS claims that she is immortal and will live forever, long after Chell has died. Is she correct?

If yes: how? If no: what would kill her first? For example, if the facility's nuclear reactors ran out of fuel, if they can.

You can answer in the context of Portal (wherein the facility is fully stable, albeit empty) or Portal 2 (wherein it is more damaged, though she is clearly able to repair it).
gpt
If her personality is pure data, then there would be nothing to stop her from copying herself onto new hardware whenever her 'body' becomes obsolete or she feels like an upgrade, or could pre-set copies of herself as backups. Even if Aperture's computer/storage tech is 100% proprietary, the building has on-site manufacturing capacity. Barring some manner of sudden system failure or massive physical attack on Aperture, she's got a good shot at outliving any human. And if she goes mobile, like she builds a core setup that could be installed in a vehicle, then not even that is guaranteed to take her out.