The future of the line rest with the Gen3. If they can sell 1000+ a year and keep people excited, Viper will be around for some time to come.
The whole Daimler thing has never thrilled me but keep in mind the HUGE investment (expense) of creating the new Viper and they surely seem committed to the SRT concept.
I think we will know in 3-4 years. If a coupe is planned, the line should stick around for years to come. If there's is no longer enough hype associated with the Viper to justify the expense, to get people talking about Dodge/DC and into the showrooms (the only reason there's a Viper in the first place), then it will go away.