We are talking about technology that literally has infinite possibilities it would also be technology that may very well violate our law of physics as we know it.
If they have the technology to get here they could do things we cannot begin to comprehend
Not true. Mathematically we know how to achieve it. The problem is we don’t have an energy source capable of achieving it. The biggest problems though are as follows
Doing so would cause so much force it would destroy every planet in our solar system. Think a sonic boom when entering the speed of sound now magnify that to equate the speed of light
Durability. Atoms break down long before even hitting light speed to not only would any vessel attempting it break apart but any organic life inside would turn to liquid slop and disintegrate.
You also need to ask yourself what’s the purpose interstellar travel would serve? If we have the ability to terraform other planets then we would just do so on our own.
Now to less than theoretical science and actual tangible problems. We have already filled the space around our planet with so much trash (old satellite’s, shuttle ejections ect) that the days and times we can safely launch a craft from earth without it colliding into something has grown rather small to a point of only 71 days of the year. The more we do the smaller that number gets.
Make that 70 as China just goofed putting another satellite up leaving a mess in lower orbit.
“We’re calling about your spaceship’s extended warranty.”
i blew that ship up and do so everytime i see it. Best part is no bounty 
They are coming. Prepare.
Even if it happened today, it would not be soon enough.