A simple majority does not provide control in the Senate. It will allow them to sneak some stuff through via reconciliation, but there's no way a truly conservative agenda can be pushed through the Senate. They'll need to find some support from the other side to get anything else through - just like the Dems needed Reps to pass their Immigration Bill.
They really need to focus on being a Republican-led congress by actually providing leadership with a productive agenda. To that end, they need to replace Boehner and probably McConnell. Boehner's track record in a Republican-controlled House is extremely poor. For example, it's fine they didn't pass the comprehensive immigration bill, but they haven't delivered on their promise of passing the portions they like. McConnell can stay IF he's learned what went wrong the last time after the 2010 elections.