Think this situation of disaster recovery, that i am recreating in my lab.

EXCH2013 installed on a server, member of AD, CAS+MB.

That server goes down, and can't work anymore.

I reinstall, on other server in the same AD, CAS+MB. I have copy of db, for example in local pst or other kind, no matter now.

When i access to ECP new  server i will be able to manage users, i will find the users mailboxes activated in other server (and not working) but i will have the chance to "recover" situation creating new users or assigning user's mailboxes on new server.

Is this right?

Why OWA, ECP, on new server DON'T permit to log (old server DOWN)? I can see the page, put the credential but then error 500...how think that IIS service want to find the MB on server down, it can't find and goes error.

Any suggest?

I would do /RecoverServer first which will recover the server. And if I have the EDB file then I will mount that data. Or if I have Backup, I will restore the Backup.

Note: Make sure all the exchange services are running after /RecoverServer is successful

Does it works with new Mailbox?

ok. but why  i can't access owa/ecp? 

Cause you haven't mentioned how did you got the server up and running? Was it /RecoverServer or just rebuild the new server and mount the database or something else?

Also you didn't answer the question, does it works with New Mailbox?

Sorry, i have done a simple fresh install 

Setup /IAcceptExchangeServerLicenseTerms
and it has installed on the same organization name.
After a get-mailbox on NEW server i can find them via cmdlet, but remain the OWA/ECP not logging state.
Teorically, i can install "n" exch servers, and each one can do the mailbox and cas role...isn't it?