Talks about setting up second production line were going on for long, dating back to last year or so, the issue was/is funding and if the deal for say mk1a gets signed then HAL will have clear order so to meet the production rate they can go for another production line.
I am not talking about wartime or anything just normal day to day work. Mk1a was supposed to come out in it 2023 or so and by that time frame they can have a working production line, I don't see an issue here.
Source :
https://www.tribuneindia.com/news/nation/20-tejas-a-year-possible-hal-chief-37648
Also, we already have the second production line while the third one is underway, don't know about its status.
2nd production line has a capacity to produce 3 aircraft per annum while first can produce 5 of them per annum.