Lost connection to mysql while restoring dump. Is it safe to resume?
(n.b. I've never used AWS or RDS so there may be some differences). But as a general rule a MySQL DUMP file is just a series of CREATE TABLE and INSERT INTO statements, that when combined create your database.

Ultimately it depends on what options were chosen as to what does and doesn't get included. But I think that by default it includes the --add-drop-table option. So if you open the file (which is basically a text file) you should see:

DROP TABLE tablename;
CREATE TABLE tablename. . .
INSERT INTO tablename. . . 


for all of your tables. 

Restarting the loading process will simply start from the beginning of the file and carry out the actions accordingly.

(I assume that the import has actually died - its not uncommon (in my experience) to lose connection to MySQL during the import due to the time taken, but the process continues in the background. You can use SHOW PROCESSLIST to check this).