The .NET team has always been on friendly terms with the Mono team. I'd imagine the Mono devs will either keep doing their thing or will merge into the mainline at some point. There's Java VMs that are even commercial, as in people pay for them. I'd imagine that there's certainly enough space for a couple competing CLR platforms.
Merge - Xamarin are getting out of the language game and instead focusing purely on mobile. As much as possible the new MIT licensed .NET will replace pretty much all of Mono that isn't Mobile (iOS/Android/Mac) related.
