2 MCA seats within the 15-man state assembly would presumably shift the balance from 13-2 to 11-4 in favour of BN.
The Alor Setar parliamentary seat would make BN 1 seat weaker in Parliament.
Gurun and Bakar Arang state seat would fall back to PR, making them stronger in the state assembly from 20-16 to 22-14 once more, making up for the 2 defections.
Tanjong Malim, Lumut, and Kampar parliamentary seat would be lost by BN. Make that 4 seats weaker in total.
Chenderiang and Jelapang state seat would fall to PR. From 31-28 in favour of BN, it will swing to become 30-29 in favour of PR. Perak retaken yeah!
Pandan parliamentary seat would be lost by BN. Getting weaker and weaker in Parliament.
Kuala Kubu Bahru and Sungai Pelek state seats taken, making PR more secured and entrenched in Selangor.
Chennah state seat would fall to PR, making BN's position precarious. From 21-15 to 20-16 in favour of BN.
Alor Gajah parliamentary seat lost by BN.
Machap, Kelebang, Duyong, and Bemban state seats go to PR. Opposition in Melaka would be stronger now. From 23-5 in favour of BN to 19-9 in favour of BN.
Labis, Ayer Hitam, Kluang, Tebrau, Gelang Patah, Kulai, and Tanjung Piai parliamentary seats would be lost by BN. Make that 13 parliamentary seats in PR hands. (BN 138 - 82 PR. After defections and by-election, make that BN 143 - 77 PR. However, if MCA leaves, then it would be BN 130 - 90 PR at this point)
Jementah, Bekok, Tangkak, Yong Peng, Parit Yaani, Penggaram, Paloh, Johor Jaya, Stulang, Pengkalan Rinting, Pulai Sebatang, and Pekan Nenas state seats would be lost by BN. From a very comfortable position in the DUN of 50-6, now BN is only leading by 38-18 in their favour, just barely holding their 2/3 majority in the State Assembly.
Raub and Bentong parliamentary seats lost. Make that 15 seats lost in total at parliament level. (BN 128 - 92 PR)
Tanah Rata, Cheka, Damak, Semambu, Teruntum, Mentakab, and Bilut state seats lost by BN. From a score of 38-4, their majority is reduced to 31-11 in the State Assembly, making the opposition more vociferous.
Bandar state seat lost by BN. Not much difference as the score would be 23-9 rather than 24-8.
MCA never stepped foot in Penang and Kelantan. I'm lazy to cover Sabah and Sarawak, as they are mostly local BN components.
So, what happens when MCA leaves? Only 1 clear conlusion, which is PR will regain Perak if MCA indeed leaves BN, that is, if they ever do of course. ;P