#2 Is there a possibility to share a single instance of Memcache between multiple projects?
Yes, because Memcache is a memory that stores space and it can be run on one or more servers. It also allows you to run two different Memcache processes on the same hosts even though they are independent.
#5 What happens to the data stored in Memcached when a server is automatically shut down?
When the data stored in Memcached and the server gets shut down accidentally, the data is already not permanently stored. It is not a prolong data, whatever happens, the data gets deleted in Memcached.
Memcached is an open-source, high-performance, distributed memory object that speeds-up data-driven websites by caching data and objects in RAM. It is an element that helps in storing data for 1 /6/12 hours or 1 day etc. it lets you integrate with your applications to procure increased performances.