Maybe this helps:
vpn tu tlist
But it is a difficult question, because if the tunnel is ''up'' with p1 p2 it still can be that for the user the tunnel is not working.
Or a part of the tunnel works and other part does not work (if you have more subnets in one tunnel).
You can check the firewall logs and check for logs from local enc domain towards remote and the other way around. Good indication is also to check logs from and towards remote peer IP.
Tunnel config also has p1 and p2 timers, most of the time if timer is reached new p2 or p1 is created.
In R82 you can configure VPN probes, those are hosts that you ping via the tunnel to check the status. Check it here:
https://support.checkpoint.com/results/sk/sk181994
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