I'm reading many of the Wikipedia pages about exoplanets and the different methods they are using to detect them. But I wonder, it seems that the emphasis is on detecting and finding new exoplanets, but are astronomers continuously monitoring the exoplanets that have already been discovered? For instance, if there is a collision between a detected exoplanet and a previously unknown planet, this could cause a change in some of the orbital parameters, and could be potentially detected. If this happens, would we learn of this change, or will it have to wait until astronomers again take another look at the system?
Exoplanets is an almost over populated field of research now, so yes they are monitored. But maybe not too much beyond what is needed to confirm their existence.
I think you have to humble yourself in the enormity of time. There are some transient events in astronomy, but mostly, watching the sky is like watching a rock. Nothing much changes. Phoebes is crashing into Mars. But not until several million years. It will be a very slow process of it breaking up and parts of it landing one by one. Even in the midst of that event human intuition would think of it as a frozen constant non-event. Like the rings of Saturn. Look at a mountain and see how fast it grows or shrinks. Astronomers cannot see exoplanets crashing into each other in the way I think you mean.