Newbie manager of a Ubiquiti UniFi network, how vital is it to replace EOL access points?

Hi, I've recently been put in charge of a network with several older access points that have been EOL'd by Ubiquiti. Not wanting to spend a lot of money at once to replace them, if I were to avoid updating the management software and firmware, how big of a risk would this be in terms of security, etc.? Could I expect them to function indefinitely as long as I don't update, so I could do rolling upgrade instead of a large purchase? Sorry if this is relatively basic.