Hello,
If your Compute Engine Instance was deleted, it is not possible to restore it[1]. During
the creation of the Instance you could configure deletion rules to keep the boot
disk when the instance is deleted. This can be configured in the submenu
“Management, security, disks, networking, sole tenancy” in the Disks section.
However, if you have a snapshot of the disk[2], you can create a new instance
from that snapshot, or, if the disk from the original instance was not deleted
(as I explained above), you can create a new instance[3] from that disk.
As a note, there are settings for preventing accidental deletion of instances[4]
which may also be useful.
Also, if you have a machine image [5], you can recreate an identical
instance from it. A machine image stores all the configuration, metadata,
permissions, and data from one or more disks required to recreate an identical
virtual machine instance [6].
I hope this makes things clearer for you and I wish you a good day.