So I wanted a way so that the script stops execution

Then eval does more or less the opposite of what you want. Instead of

eval{$elem = $driver->find_element(".//*[\@id='nav']/li[3]/a");}
[download]

you could try

{
    use warnings FATAL => 'all'
    $elem = $driver->find_element(".//*[\@id='nav']/li[3]/a");
}
[download]

However, that's just a guess, and the use of "fatal warnings" is controverse.