I don't want to write so long. Just some words about Lahiru thirimanne. He is not successful in Test and T20 cricket. But what about ODI?
In last 2/3 years, he is one of the most consistent players in ODI team. Specially in opening position, he has done some great performances. As Dilshan retired, who can be better opener than Thirimanne.
Opening and one down position, his average around 40. In 2014/2015, his batting average is more than 40. In world cup, he showed a very decent performance with the bat.
So, his failure in test or t20 doesn't mean that he should be out of ODI also. As dilshan, Sanga, Mahela retired, Thirimanne can be one of the backbones of Batting line up.