[reddytowns]

How about:

The old version of this code is under source-control <here>. The code is very complex and likely to have subtle bugs. If bugs _are_ found, it might be of interest to look at the old code and see what did it do in the relevant situation.

[gaius]

Where is <here> and will it always be there?

[V-2]

What is "always" and do we have to care about always? Sounds like splitting hairs to me.

Even the comment in question admits: "it's true that it will be accessible from the repository".

Only then it goes on to say "but a few years from deletion, people will forget it is there" - well, then just leave a comment reminding them about it.

I see no plausible reason for keeping dead, commented out code in the codebase when you've got VCS.