What are the possible implications of parallel block chains developing. For instance if a country or significant subset of people got isolated for a substantial period of time, they would surely start work on their own block chain. When this isolated group was then reconnected to the rest of the network then, assuming that they did not hold the majority of the processing power, the block chain they had been working on would be destroyed and all transactions placed in that time lost.
This may be unlikely to happen but if it did then:
How would it be detected, as the bitcoin client only has a handful of connections to other nodes and does not need connections to every other node so a decrease in the total nodes available would not really be possible. Looking at how bitcoin tries to find other nodes there would probably have to be some malicious activity involved to keep fake irc/dns records but may be possible through 'natural' causes.
If this did happen and the resulting lesser block chain was valid. How would these transactions be recovered if at all possible?
This doesnt sound beyond the realm of possibility and if isolations happened often( malicious or natural ) then this would surely seriously affect the reliability of any bitcoin transactions placed.