What will happen, if those projects are not migrated because their developers have simply forgotten about them?
Could you publish a list of projects w/descriptions? That would be great for others (gitlab?) who might want to host / cherry-pick / curate the collection a bit more than that.
Deleted comment
E.g. MIT:
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to
deal in the Software without restriction, including without limitation the
rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
sell copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
IN THE SOFTWARE.
Comply with those terms (i.e. include that piece of text when you redistribute) and you satisfy MIT.
GPL, &c, they all have similar clauses. In fact, MIT goes much further. I could take all those projects, mirror them, and charge people insane amounts of money for it.
If you can't even rehost on Github, what good would copyleft be?
(now, third party code they may have included is a different issue, you can't get rights to that through someone else's claims, but ...)