Infiltration and shooting, How does re-stealthing work? Options

[Elfenlied]

So, assuming you're hidden with an infiltration roll (4 successes), and attack someone with your silenced Ares Predator. The target survives.
Now, do you:
a) Let the attacker use his remaining simple action to re-stealth (another infiltration roll), and the target gets to roll perception on their IP, with the -4 due to silencer, or
b) the attacker can spend his remaining simple action to do whatever he wants, and the target gets to roll perception on their IP, with -4 due to silencer?

Also, are there any other modifiers/rules I should be aware of? Because, from my understanding, it would be way too easy to chip away someones health utilizing a silenced firearm, while remaining stealthed.