Safe method to rename a crashed myisam table
This might work; do it with caution:

CREATE TABLE new LIKE real;   -- copy schema
RENAME TABLE real TO bad, new TO real;  -- replace broken table with empty
REPAIR TABLE bad;     -- slowly repair
RENAME TABLE real TO old, bad TO real;  -- replace empty table with fixed table
DROP TABLE old;   -- clean up


I don't know if the CREATE will work with a broken real.

The RENAMEs are 'instantaneous'.

Then schedule moving to InnoDB.