More than likely you'll need to push your ISO and add additional light befor you need to buy a faster lens. Using an F2.8 or F2 lens wide open will admit more light, but your depth of field will be thin. For events it's usually better to go to F5.6 or smaller, even if that means you need to shoot at ISO 6400 or higher.

Beware of flash domes and card diffusers if your distance from light to subject is more than a few feet. A dome at 10 ft or more is not all that different than an unmodified speedlight - and in a big space without the benefit of bounce surfaces, will provide harsh shadows. The same goes for bounce cards - even the Rogue Flashbenders are not going to provide flattering light if the distance is too great.

This guy has some great advice on how to provide natural-looking light with speedlights for event photography.

https://neilvn.com/tangents/high-iso-bounce-flash-photography/

Consider renting the 35mm 1.4L. Indoors it has the "speed" in low light and is a good focal length for groups of people and half body portraits. The 24-70 f2.8 is the general "go-to" lens for indoor events. The best use for you 70-200 would be it there's a dais and there will be speakers and awards presentations that you could shoot from the peripheral. (Be sure to get an agenda from the organization so you can know what's going to happen). Another tip - arrive early and shoot the preparations - it will give you a good feeling for the lighting and will give you an opportunity to get to know the organizers for future events.

Last weekend I saw a 5k mud/obstacle race and took my camera just to be doing something, I was at the finish line catching runners cross when the director of the event came up and gave me her card and ask for the photos, seemed real upset with her Photographer, said he was suppose to be covering that area but he was off playing with his drone.

That night I sent her the pics and she seemed to really like them and ask if I was available to cover a Gala there doing. Now for the question, it’s a late evening, indoor event and the location has dim lighting for these events. I only have a 24-105 f/4 lens and a 70-200 f/2.8. I think the 70-200 will be to long and I don’t think my 24-105 would be good with the lighting with it being an f/4. I’m considering renting or just going ahead and purchasing a 24-70 f/2.8. Flash and setting up lights isn’t an option here. Do y’all agree or do y’all think my 24-105 would handle it?

I usually do all my work outdoors and with natural light but I don’t want my equipment to limit me. I’m shooting with a Canon 5D mark iv. I have done indoor, lowlight work with my 70-200 and was happy with the results but never worked with the 24-105 in these conditions.

Last weekend I saw a 5k mud/obstacle race and took my camera just to be doing something, I was at the finish line catching runners cross when the director of the event came up and gave me her card and ask for the photos, seemed real upset with her Photographer, said he was suppose to be covering that area but he was off playing with his drone.

That night I sent her the pics and she seemed to really like them and ask if I was available to cover a Gala there doing. Now for the question, it’s a late evening, indoor event and the location has dim lighting for these events. I only have a 24-105 f/4 lens and a 70-200 f/2.8. I think the 70-200 will be to long and I don’t think my 24-105 would be good with the lighting with it being an f/4. I’m considering renting or just going ahead and purchasing a 24-70 f/2.8. Flash and setting up lights isn’t an option here. Do y’all agree or do y’all think my 24-105 would handle it?

I usually do all my work outdoors and with natural light but I don’t want my equipment to limit me. I’m shooting with a Canon 5D mark iv. I have done indoor, lowlight work with my 70-200 and was happy with the results but never worked with the 24-105 in these conditions.