You'll want to make sure the vmkernel interfaces are backed by system VLANs on the 1000v (as opposed to regular VLANs). System VLANs are fully functional in headless mode, whereas you have some limitations on regular VLANs. In a nutshell, with the VSMs offline, existing connections will be maintained for ports backed by regular VLANs, but new connections (including reconnects due to VM restarts, or host restarts) will fail. See this for more info:
http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9902/guide_c07-556626.html#wp9000293
If you have sufficient uplinks available, another option as you mentioned is to use a VSS/VDS. Either way, don't forget to protect your VSMs' vNICs as well as the vmkernel interfaces.