If someone from the future fixes LC it creates a paradox. Always. According to Vadderung this causes a split in the timeline. Whoever goes back can't change their future. They can only create a new future where Harry doesn't kill himself with LC.
It's like a murder investigation. Who has means , motive and opportunity? Since Harry was keeping LC under wraps before first use, who could have known of it existence in the present? That list is small. Maybe Mab and/or the Gatekeeper. It's never explained implicitly, but Mab has some means of seeing what happens in Chicago. She reproduces a past event in Chicago, in full animation, in Small Favor. And the Gatekeeper has showed the ability to find Harry wherever he might be. He does it in Summer Knight and Turncoat. However the ability to be able to do so removes the need to use LC, since she/they seem to already have a more powerful tool that does the same thing.
However, Mab might fix LC to fulfill Lea's obligation to protect Harry, since in Proven Guilty she is restrained and as of Dead Beat Mab is filling in. This WAG depends on the exact nature of Lea's obligation. However we do know that she kept a garden in the Never Never to keep enemies from entering Harry's home past the threshold. This means that Mab had a private doorway into the sub basement. So this a possibility. That is means and motives.
Opportunity. Anyone monitoring Harry would know when he and Bob were both out of the apartment. Again this fills the bill for Mab/Gatekeeper. Bob is not in the basement for most of the events leading up to the raid on Arctis Tor. So the basement was free from surveillance. Anyone with the means to enter, could do so without interference.
Since I don't like time travel I won't discuss it other than to say that anyone in the future possessing Bob, assuming he survived, would have everything they need to fix LC if they could TT.