Microsoft Dynamics 365 offers a financially backed 99.9% uptime SLA, as described in the following article:

http://go.microsoft.com/fwlink/?LinkID=196557&clcid=0x409

High availability is achievable through geo-redundancy, as described later in the Data redundancy section.

Only one site is primary at any one time. Upon a disaster, the secondary site takes over. From an enduser's perspective, the switch is seamless and automatic.

More recently, Microsoft announced multi-site read capabilities to improve performance using load balancing.