Question about subpoenas and impeachment

Trump is fighting subpoenas all over DC, a lot of them germane to the impeachment process. Now there is talk of referring articles of impeachment as soon as next week. It seems to me that nothing should be filed until at least some of these challenges are resolved. If they proceed without testimony from key people, and without mounds of incriminating documents, then McConnell simply hold pro-forma "trial", votes to dismiss, and its over (He has the votes, the GOP has made it clear they will not oppose Trump no matter what he does). At that point they will argue that all the subpoena questions are moot, and should be dismissed, meaning Trump successfully obstructs justice and walks.

Can someone enlighten me on what happens to these cases of the Dems go ahead and refer the case to the senate where it is summarily disposed of?