Both Jayawardene, who went unsold at the just-concluded players' auction for the seventh edition of the Indian Premier League, and Herath returned from Bangladesh having missed Twenty20 and One-day international matches there due to injuries.
Thirimanne returned home from the United Arab Emirates last December midway through playing Pakistan.
Uncapped seam bowler Chathuranga de Silva will take Herath's place if the senior doesn’t recover in time for the tournament, starting March 16.
Sri Lanka will have four specialist spin bowlers if Herath returns, including all-rounder Sachithra Senanayake.
There are eight specialist batsmen, including seam bowling all-rounders Angelo Mathews and Thisara Perera.
The Asia Cup, also in Bangladesh, precedes the WorldT20.
Squads:
WorldT20: Dinesh Chandimal (Captain), Lasith Malinga, Tillakaratne Dilshan, Kusal Perera, Kumar Sangakkara, Mahela Jayawardene, Lahiru Thirimanne, Angelo Mathews, Thisara Perera, Nuwan Kulasekara, Suranga Lakmal, Sachithra Senanayake, Ajantha Mendis, Seekuge Prasanna, Rangana Herath or Chathuranga De Silva.
Asia Cup: Angelo Mathews (Captain), Dinesh Chandimal, Tillakaratne Dilshan, Kusal Perera, Kumar Sangakkara, Mahela Jayawardene, Lahiru Thirimanne, Ashan Priyanjan, Thisara Perera, Lasith Malinga, Nuwan Kulasekara, Suranga Lakmal, Sachithra Senanayake, Ajantha Mendis, Chathuranga De Silva.
Image: Mahela Jayawardene
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