There's no particular onus for a replacement. Content is always at the whim of the content owners and in this case the owners (Not FetchTV) took their content elsewhere. Content providers like Fetch do highlight that the channel lineup can vary (for better or worse) any time.
I'm sure Fetch are looking for other content but in practice it will be completely different shows. Until then I would say evaluate their product on what it is offering now.
These are the last two communications we have received from Fetch about their channel changes:
I can confirm @Harrison observation. Apparently SyFy is due to end in 28 days. FetchTV are showing a small B&W note in the EPG and its also noted on their packages on their website. Yet just seven days ago FetchTV announced several Disney channels were closing but explicitly stated no changes expected for the SyFy channel. All FetchTV recordings for this channel will be deleted in 28 days. Fetch and Optus have done well communicating these changes for 13 Street and Style but I the major channel of SyFy has been badly managed to date. There's no legal requirement to stay on stop of channel changes but telling people its going, no its staying, actually its going is not a great process.
@Ray_YC - I reckon someone at Optus needs to get on to the phone to someone at Fetch?
Fetch also have a Kids Disney Channel which I assume is under contract for the content at the moment but assume that will also be withdrawn at some point in the future.