Re: What happens if BU fails VS What happens if SegWit fails

1. BU does not cause bilateral fork. LEARN CONSENSUS

Yes it does cause a split. You are mistaken.

He is mistaken, but for different reasons. BU is a unilateral split. If, after BU pulls the trigger on their hard fork, the Core chain ever overtakes the BU chain, all BU coins will be permanently destroyed and all transactions involving them will be forever invalid. Mass panic will ensue and their altcoin will be worthless. That's why Core devs are begging BU to make their fork bilateral, but they won't listen (or they pretend not to listen because they don't have the competence to implement a bilateral fork).

if BU pulls the trigger.. it would do it with majority NODE (over50%) and majority hash(over 50%)
it wont trigger without consensus.

You are seriously confused about this aspect. There is no "majority hash rate consensus" between INCOMPATIBLE CHAINS. The only thing you do with your 51% hash rate is to produce INVALID BLOCKS wrt the original protocol. So this PoW doesn't matter, the blocks are invalid. If you produce 1.5 MB blocks with a PoW that is more than 10 times all the PoW that ever went into bitcoin, then these blocks doesn't count because they are simply INVALID. The old protocol simply rejects them (in the same way as if they were containing wrong signatures in the transactions). The only valid blocks (wrt the old protocol) are those, mined with the 49% hash rate of the miners sticking to the old protocol.

But the new protocol can continue building on its own chain with bigger blocks.

Non BU blocks are still 100% compatible with BU so if BU doesn't have more than 50% of hash power, the fork will fail untless BU miners intentionally filter the non BU nodes. The only way for a fork to be successful is if the BU miners mine a block > 1 MB and have 51%+ of the hash power. Personally I'll wait until 18 blocks longer before I really consider the fork successful.