Snape's Duty in the GoF

[maria_mcnally_2003]

No: HPFGUIDX 34985

After finishing the fourth book yesterday, I was a bit curious what 
was Snape's duty since he replied to Dumbledore that he knew what he 
was going to do.  Is Snape going to be a spy or will he be killed by 
LV.  During the part when LV talks about who betrayed him, he 
mentions Barty Crouch (who is innocent) and two others that will be 
killed..one of course if Karkarof (sorry if I spelled this wrong) and 
would the other be Snape?

As a result from Mr. Crouch being killed, will Percy take upon his 
duty?  Also, what are other purposes for mandrakes.  In the previous 
book in CoS, they were used to bring ppl to life (such as Filch's cat 
and Hermoine).  Will mandrakes ever serve a purpose to bring someone 
back from the dead?  

Maria