in the event of a situation in which a majority of representatives are suddenly unable to serve?

There is a detailed line of succession for the presidency. Vice-presidents can be replaced also, under the 25th Amendment. Senators can, I believe, be replaced by the governor of their state if there is a death, resignation, etc. But as far as I'm aware, the only way to replace a congressman is through a special election, which always takes time.

Shouldn't we have some kind of procedure for replacing congressmen, even temporarily, in the event many of them are suddenly unable to serve? Yes, I am thinking of a terrorist attack, among other things. It's possible that we could be left without sufficient leadership just when we needed it most. Those concerned about presidential power should also want a way to re-convene the House as well as the Senate quickly, also.

Does anyone know if there are any laws already in this regard?

Thanks.

We already have that the Governor of a state appoints someone it used to be the Gov. would appoint both Senators which was a huge gift.

There are actually already protocols in place to rebuild the government in the event that something should occur that decimated the ranks of any of the branches.

"I am happy to report that TWO of your three branches of government are still functional, and that AIN'T bad!" ~ Jack Nicholson, "Mars Attacks"

The Senators and Congressmen are elected by the respective states. Federal Law does not govern how they are selected, State laws do. Every state already has a contingency rule in place. Usually, the Governor appoints one until the next election.

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You raise a very important concern; I am not aware of any plans in place in the tragic event that we lost a lot of members of congress. A well-timed nuclear attack on DC could very well leave us with no leadership. That would be horrible, and so is not having a plan to deal with such awful unexpected events. Something needs to be put in place; maybe the runner up in the election for each seat would be on board to take the current incumbent's place in the event something happens? Any type of special elections would take time and be chaotic, and I am surprised no contingency plan exists in the event of a terrible emergency that would leave us without leadership.

Edit: apparently I am wrong, a plan does exist, but I think something should exist in the event that many congressman are lost at one time. Each state has their own rules, and I think policies should exist that govern what happens if many of our officials were lost.