If one node has new version number with some revised source, then all chain network follow it? and recognize all themselves as obsolete?
If this is true, how to preserve past balance and record?
No. Following is my ELI5:
First of all even if core repository got wiped or infected - nothing will change since auto update is deliberately not implemented in core. every individual in BTC network have it's own "voice" and "mind". Mind decides what to follow and voice decides format of communication with the rest of the network. You can create your own client that mimics currently standard mid and voice or you can break either. If enough people decide to update either of the above - rest of the network can decide to follow (this will result in soft fork) or not to follow (this will result in hard fork).