Fault tolerant E1 with Asterisk

I have two asterisk servers, one with 100 users, and other one with 150 users. Both server are on the same building (one is on first floor, other on third floor). Both of them have a E1 line (for historical reason, I have an E1 line on each floor).

My question is: Could I setup the Asterisk on third floor so if the E1 has a failure, external calls are routed to the E1 on the other Asterisk ? Of couse, both Asterisk will have a direct local network connection between them, and since both belong to the same business, being able to connect each other.

Does DUNDI makes sense on this configuration ? Could one Asterisk act as backup of the other one ? Could be on E1 be assigned as backup of the other one ?

My intention is to ask the PRI ISDN provider to setup them so if one the PRI is broken or full, new incoming calls will be redirected to the other one. And I want to have the same efect on outgoing calls.

Any suggestion will be apreciated.