What happens when a fork/network split occurs on the Stellar network? Say some country decides to somehow block all outgoing Stellar connections for 30 minutes. With a voting based consensus that Stellar has chains in both networks progress with a similar speed. After the network split is over there will be two Stellar networks with a diverged history.

How would such an outcome be resolved/avoided with the new consensus changes? Is there some way to determine which network state is correct after the split? Can the smaller split network know that it's split and pause accepting transactions?
Assuming people chose adequate quorum slices and the system has quorum intersection (which is how the system is intended to be used), then with Stellar's new consensus protocol, at least one of the two partitions would be unable to settle transactions for the duration of the network outage.

Stellar does allow for redundancy, in that validators can have multiple slices.  For example, a slice might consist of any 5 out of 7 validators spread across countries.  In that case, if the partitioned country has only 1 or 2 validators, the rest of the world can continue to make progress.

This kind of scenario is actually unavoidable.  You have to chose at most two out of Consistency, Availability, and Partition tolerance.  This is sometimes known as "Brewer's theorem" because Eric Brewer conjectured it and Seth Gilbert and Nancy Lynch subsequently proved it.  See: http://www.cs.luc.edu/~pld/353/gilbert_lynch_brewer_proof.pdf