Tommy_Tickle, You are correct in your choice. You will Clear Foreign if array is working, or Import Foreign if array is offline. Since the OS isn't booting you will import. You should see some results almost immediately upon Importing the foreign. You should see one drive go online, and the other start rebuilding. Although the Virtual Disk would be rebuilding for a couple hours, you should be able to boot the OS right after Importing.  If not then let me know  
I am not our IT expect, but am relatively competent, just not to a recognised professional level I suppose, so we outsource that stuff and although we have a chap looking into it, he is slow, hasn't really given me an answers he has't blatantly just got from Google right in front of me, and then he disappears for long periods, so I thought I would post here in the meantime, so here goes. We have a PE R510 with x2 RAID 5 channels containing x6 600GB SAS disks in total, so x3 disks each channel on a PERC H700. We came in Monday morning to a non-responsive server and message on the screen reading: There are offline or missing virtual drives with preserved cache. Please check the cables and ensure that all drives are present. Press any key to enter the configuration utility. Visually I could see 3 discs showing warning lights, disks 2 and 3 in the first RAID channel (RAID 0) which is the OS only, more or less, and disk 5 in the second channel (RAID 1) – which is the bulk of the data on the server. I’ve since replaced disk 5 with a new disk and RAID 1 has successfully rebuilt, but RAID 0 is still down and I have no OS to boot to – so am still locked out of access to the data. So, concentrating on RAID 0 I established disk 2 was blinking green two times per second which suggests a ‘preparing for removal’ status, disk 3 was blinking green and amber, suggesting a predicted fail. Turning quickly back to the IT expert, he has now gone away to get tools etc. with the plan of coming back and taking the server away so he can the recreate RAID 0 with new disks and reinstall an OS on it, however, in the meantime having looked through these forums I’ve had a sniff around myself. If I go into the PD MGMT on the H700 screens this tells me disks 2 and 3 are marked as Foreign, with disk 1 showing online. Several suggestions here seem to suggest in such instances we should be using the Import option to import this config. to the array. In my mind if the plan is to have the server taken away to have this RAID recreated from scratch anyway, we’ve nothing to lose by giving this a go - with the one exception of time, does that sound right? My question is then, given the above – how long might it take to see if the Import function works? If it is likely to take several hours, I may as well just let the chap take the server away for a day and come back with a new OS installed tomorrow, but if this import function is likely to get me into the OS within an hour maybe 2, tops, for example – it might be worth a shot sitting and waiting. I eagerly await the forums advises. Thank you in advance.
PowerEdge R510 RAID 5 Foreign Disks Question