according to CVP 3.1 SRND survivability is not supported on a standalone scenario.
Anyway, if CVP is down or unreachable,
I should be able to get in touch with a
predefined IP-Phone extension.
Is it something we can do on Voice Gateway configuration?
Survivability.tcl can be used as well?
Any help will be apreciated.
first of all you have the option of deploying a Gatekeeper and if the CVP is down return the call to the gatekeeper to send it straight to a call manager extension.
If I recall it right in your scenario you don't have a GK, I think you could try to play with the dialpeers priority and have a second dialpeer available in the event the CVP is not, this has some issues that you need to carefully monitor, if your solution is taking more calls then you designed it for during peaks then this lower dialpeer will try to route calls that would otherwise be treated by the CVP side.
Third alternative is using a custom tcl script as you suggested, but it would not be easy to overcome the same limitation recommending not to deploy it in a standalone environment.