However, if you have foreign key constraints such as RESTRICT that ensure referential integrity with other tables, you'll want to drop those keys prior to dropping or truncating a table.
Yes it would drop the index. There's no reason to keep the index if the underlying table isn't there. I suspect that the downward migration is just doing the opposite of the upward migration on a one-to-one basis.
It is unneccessary. Your DROP TABLE might however be prevented when the table is part of foreign key relationships and dropping your table would break the dependencies.