I cut the wires too short to attach back on the HO ballast so I can't use it unfortunately

Do you have any spare wire around you can borrow, perhaps from a cheap ballast, extension cord, NM cable, etc.?  If I don't have 18 AWG I'll sometimes splice in either 14 AWG or 16 AWG in the middle, then back to 18 AWG at the sockets since most of them only accept 18 gauge. 

Is it that you cut the leads back too far to ever re-use the ballast, even if you could the a hold of additional wire?  I've often stolen wire from one ballast in order to hook up another, but I try to leave enough to still reconnect it in the future.

I cut the wires too close to the ballast case so it is unusable

If there's enough to strip but not quite enough for a wire nut, maybe you could get a Wago or other push-in wire connector.

Even if the lamps lit on the HO, that wouldn't prove the VHO ballast was fault considering electronic ballasts tend to have more success starting faulty lamps.  However, if impurities or poor lamp conditioning is to blame, some run time on the electronic ballast might enable them to start on the magnetic ballast again.  If the problem is partial vacuum loss, then they'd likely degrade further and eventually fail to start on the HO electronic.  That'd be unfortunate, but at least you'd have your answer.

Provided the cathodes are being heated, there's probably no harm in letting them sit flickering for a while.  Perhaps they'll eventually fire up.  That being said, if one of the cathodes isn't being heated, the result will be irreversible sputtering.  Another option is to try the opposite and leave them off for a while.  I'm unsure why, but I've had some troublesome lamps in the past that seemed to become easier to start after being left off for a day or more, although I'm a little unsure why this is the case.

I presume this is a series ballast, right?  I wonder if there's another kind of lamp you could put in series with the PG temporarily to test them individually.  Perhaps somebody here would know what might be acceptable for a quick test.

Also, I know you've checked everything, but I would again inspect every lead wire from the ballast to the socket and also make sure the lamps are all snug.

I just wired the ballast for 1 lamp operation and the one tube works.

I'm assuming you shunted the ballast for single lamp operating...wiring the single lamp between the red and blue pairs on the ballast, which results in a increase of OCV for that single lamp as it doesn't need to strike two lamps at once. As for the HO ballast, unless you cut the wires right where it enters the case, you can probably still attach a WAGO inline connector to it, or splice and solder wire extensions to it.

I presume using only one lamp will stress the ballast so it wouldn't be good to leave it in that state for any length of time, but did you check both tubes that way?  Although it won't prove what's wrong if either works independently, if the other one doesn't light that would suggest it's the problem.  If they do both work, then I'd try wiring it back up for two-lamp operation and seeing if they'll now start up together.

No, the ballast says it can do one lamp operation if you cap the yellow leads which I did in this case.