is there a way to protect a lsagent installation to be deleted by people who are admin on their laptop? Like a password protection or something else?
There's a bit of irony in this question. The "password" to protect against uninstalling the software is to not have people be admins on their laptops. It's literally the built-in way within Windows to prevent such a thing from happening.
My rant aside, there is no way to implement such a thing solely for lsagent, however if lsagent shows up in add/remove programs you can set up an auto deployment against a dynamic group that kicks off when the software is not detected. This of course requires that the devices in question are scannable without the agent, so it may not work depending on your situation.