I cannot speak for Imply or Metamarkets. I am not a lawyer nor am I
dispensing legal advice. As someone deeply involved in the Druid
project, what I can say is that the Druid project is licensed under
Apache v2, it has been licensed that way for a while now and there was
a very public press release regarding the fact that it was licensed
under the Apache license:
This is even linked to off of Metamarkets' own "Media Coverage" page
Once code is offered via an open source license, you are allowed to
use that code according to the stipulations of that license. While
Metamarkets could choose to take its future development of the project
internal and not share it anymore, it cannot retroactively choose to
"un-license" the code nor can it stop other people in the community
from contributing to the open source project.
Furthermore, if you are still worried about the safety of using the
project, you can send direct questions to firstname.lastname@example.org
and hopefully they can provide some extra assurances.