Join via Browser: Some companies do not allow Zoom to be installed, but users can join from the web. If possible, when the person clicks to join the Zoom they will see a dialog pop up to launch Zoom. If they click the "Launch Zoom" text they will brought to a Zoom window. On this window if they click "Download Zoom" it will actually give them an option to join directly from their browser. Many times joining from the browser is possible as companies might not want Zoom app installed.
Join via tablet or phone app: If they have access to a tablet or phone with the zoom app installed, they could join from that device and still participate fully.
Dial in: While they won't have full access to any slides or other resources added to Filo.co, they can always dial into the meeting directly via their phone and participate in audio. You could also provide a link to your slides in the room itself so they can at least download them to follow along. You can pull the dial in information from the meeting within Filo.co.