Your ASM disk group will be vanished for some reasons
if you try to mount it you will get an error some thing like the below
SQL> alter diskgroup DATA1 mount;
alter diskgroup DATA1 mount
*
ERROR at line 1:
ORA-15032: not all alterations performed
to do so issue the below command
oracleasm scandisks
and then bring the diskgrop online.
SQL> alter diskgroup DATA1 mount;
Diskgroup altered
Done..!!