Solar system escape velocity is about 5.5% of c according to a quick web search. So ca. 3000 years for 100 ly, allowing for acceleration and deceleration. The aliens would be fanatics to still be interested after that time.
But in order to come to rest here, they'll have got around the laws of thermodynamics and the momentum-kinetic energy relation to produce engines with impossibly high specific impulse, thrust and efficiency.
What we'd do is watch them whizz past.
Have you taken into account the relativity of time? If i've understood it correctly, time stops at the speed of light. For an alien travelling at that velocity, moving from one end of the universe to the other will take no time at all! No fanaticism required. How will they have time to stop? Also, does anyone know if an object with mass even move at the speed of light?
The speed of light is far too slow. If they exist (might or might not, either way is extraordinary), they are probably too far away to even know we are here (100 lightyears at the most, and probably less considering how fast radio weakens ), and then even longer to get here.
In short they can't get here in anyone's lifetime.