What the stock will be trading for in the coming months is less relevant for determining whether to tender or not than what the stock will be trading for immediately after the tender. Since you claim to be an expert on future stock prices (otherwise you wouldn't make such a bold prediction): what will LBTYA's price be on September 8?
Not claiming to be an expert. However, I have seen a few good things happen in the last few weeks. Earnings, Up-tick in M&A and the 1 billion tender.
What the stock will be trading at on 8 Sep is not important for a long holder. The share price will be a function of how many shareholders decide to tender and at what price range. I think I can get $27 for my shares toward the end of the year