As taken from an email response from one of the In Hiatus members:
The pay structure is based on a percentage of sales. For Shards Vol 2, there are 6 stories and each title will receive 10% of sales, that 10% will be split evenly between writer and artist.
After Shards a new contract will be signed, and the expectation is that the titles will then be released as individual IPs. These too will be a percentage of sales at a 60/40 split (60 going to the creators).