I can confirm from personal experience at least part of what's listed in the wiki page that DCShannon linked to:
When you return to Keely after igniting the gas from the vents, she will tell you that she intends to destroy the research data. If you have the files she'll discover they were downloaded. You have multiple options from here:
So igniting the gas will not affect your ability to get the data - assuming that you survive! However, as the summary paragraph above suggests, helping Keely will affect your options with respect to completing There Stands the Grass.
What I did, on multiple playthroughs, was choose this option.
* Tell her the truth and destroy the codes for good Karma. If she lives you will get caps or Karma depending on what you bartered with Dr. Williams.
Since you mentioned Veronica's companion quest, I Could Make You Care, there is an option specific to the combination of the two quests.
* If you are on the Veronica's companion quest I Could Make You Care, you will have another option to save the data without bloodshed. If you tell her Dr. Hildern sent you, you can say that your friend is part of a big organization that can use this data to help people. She will then state that you have given her no reason not to trust you and will open the door for you. Note that it will only pop up anytime after you find Elijah's data, and then settle for going after the data as your then central objective for the quest.
There are several other options, some similar to the two above and others on a somewhat different path. To answer your precise question, you will not need to re-download the data (that's not an available choice), but you may find that you need to approach something differently once you choose to help Keely.