First of all - these warnings might indicate that some dataloss occured - make sure to create backups of the remaining data (e.g. diskdumps) if you have not done so until now!!
* The warnings printed indicate that a disk (/dev/sda) in your system was resized (less than half of its size)
* How did that happen?
* it seems that there are some multipath devices present on this machine - but no multipath config is present in the initramfs
* what kind of disks are in the machine - is it connected to any kind of SAN? (iSCSI/FC/SAS)?
else - if half of the root disk is gone - I'd suggest to install freshly and restore from backup - but in that case it could also be just a misconfiguration on side of your SAN?!