The ship in question is a massive matter-antimatter annihilation powered starship, built by an imperialist and tyrannical government with basically unlimited budget.
The interstellar long-haul ship, is a matter-antimatter beam-core powered ship, burning diamagnetic anti-hydrogen snowballs and normal liquid hydrogen.
The tractor section is made up of two long, rectangular radiators in parallel, with the reaction mass tanks (liquid hydrogen) between them. At the base of each radiator is the antimatter storage, accelerator and reactor chamber. They are both aimed ever so slightly away from each other as to not cook the truss.
The cargo section is towed four kilometers behind the main engines, on the end of a ceramic tile-cladded rigid truss. The forward bays are for main and backup computers, control systems and docking for autonomous maintenance drones.
Behind it are the cargo modules for repair parts needed for the journey, and at the very back is the cargo space for the measly 300 tonnes of cargo capacity, of which most is just dedicated to the planetary decent vehicle, and the transport of the 20 gram sample of the Bio-mechanical Terraforming Agent, the Typhon.
In the rear are the three shield-mirrors that are docked to one another, and reflect the petawatt-power hyper laser powered by a dyson sphere from earth, which drives the photon sail.
As the ship departs its orbital docks, it will be pushed a safe distance from Mercury's orbit, where it will extend its photon sail, which is anchored to a mast between the radiators, which is a section of the truss that extends the entire length of the ship.
It will accelerate at a comfy 2 gravities until the particle-photon laser can no longer beam power to the sail, accelerating to a comfortable margin the speed of light in the process.
At this point the drones will fold the photon sail up and stow it in the cargo module for ship parts. After everything is secure, it will engage its antimatter engines and start accelerating, starting at less than 1 gravity and pick up speed as it burns though roughly 20% of its fuel and achieves its target 0.7C
Finally, the drones will detach the shield mirrors from the rear of the ship and position them hundreds of kilometers ahead of the engines, to vaporize and disperse any interstellar dust it hits.
It will now coast for the next 4 decades, traveling around 30 lightyears to the destination star system.
On arrival, the shields will be reattached and antimatter engines will fire once more, starting at 2.4G and ramping up to 5G at the end of the burn, sliding into orbit around the star.
After its payload is deployed, it will be repurposed as an interplanetary ferry, or a gas harvester, as needed.
The ship runs on the most efficient engines reasonably possible to build, anti-hydrogen snowballs and molecular hydrogen reaction mass. I haven't taken the time to calculate the exact quantities of fuel needed, but around one kilogram of fuel and 5 thousand metric tonnes of reaction mass will be used in its engines.
As if this wasn't hard enough for a much more advanced humanity to build, they built 8 of these.
For the sake of argument, lets assume the fuel tanks are about 80% full, and we still have a kilogram of antimatter.
Two of these ships were sent to each star system, as at least one of the eight wasn't expected to survive the crossing, and forty odd years is a lot to gamble with.
What if an unfortunately angled speck of dust misses the hit-shield ahead of the ship, misses the engines and truss, and punches a hole in the control computers on the forward bays of the ship, ripping a big hole in it.
The computers fail and the delicate matter-antimatter reaction spirals out of control. What will happen?
If the engines were to explode, what would happen? How much of the ship would be vaporized? How big would the blast be? What would it look like for the curious oligarchs that payed for this, though a telescope back on earth? How bad would the gamma flash be to the rest of the ship? Is there an off-chance that little lander carrying the specimen could do an injection burn and pull around the star, slamming into the planet anyway?
I know I'm only supposed to ask one question, so the question is: What will happen?
Might as well ask as much as I can, so I didn't waste your time reading this. Thanks!