Yes there would be renegotiation if the rebels were lost, but given the way value has been assigned in the past and the intent from super rugby to make up the content shortfall it's unlikely the drop in revenue would be as much as the rebels annual grant.
I think Wilson is spot on.
My two cents worth on the broadcaster situation.
With so many streaming platforms now out there I assume the retention of subscribers becomes as important if not more important than new subscribers due to market saturation.
The work Stan is doing in expanding the rugby content through Super W, Sevens, Premiership Rugby, W 6 nations, Super Aupiki, Club rugby et al, will possibly ensure that they retain more than they lose if Rebels fall away, and may even attract a couple of new subscribers to soften the blow of what they lose if the Rebels fall away.
I do not think the argument for them would be about the amount of content Super Rugby provides but rather the loss of "Rebels" subscribers for want of a better phrase, against what they pick up with what you would assume would be cheaper cost options mentioned above.