AB InBev (ABI) said the revised terms were final, which under British law means the price is set, unless the bidder drops its offer and waits six months to make another.
However, Aberdeen Asset Management
Bernstein Research beverage analyst Trevor Stirling said SABMiller's shares would probably drop to 41.50 pounds if ABInBev's takeover bid failed.
"The broader base of shareholders can take the money and run.... or seek to call ABI's bluff," said Bernstein Research analyst Trevor Stirling. Another analyst likened the situation to a game of chicken that ABI was trying to head off.
The world's largest brewer, seeking to secure attractive markets in Latin America and Africa by taking over its nearest rival, also improved the terms of an alternative share-and-cash offer designed for SABMiller's two largest shareholders.
The slide in the value of the pound following Britain's vote to leave the European Union has made the deal less attractive for all the other investors, while the rise of AB InBev shares in the past nine months has made the alternative option more so.
The new offer values SABMiller at around 79 billion pounds ($103.6 billion). In November, when the original bid was officially launched, it was worth around 70 billion pounds, or$106 billion based on exchange rates at the time. That original bid had since dropped to about $100 billion. The share and cash offer, designed exclusively for Altria and Colombia's Santo Domingo family who together own about 41percent of SABMiller, had been worth less than the all-cash option last year, but with the fall of sterling and a rise of ABInBev shares, has since surpassed it.
For a foreign dollar-based investor, the cash offer had dropped 12 percent since the British referendum on June 23.Meanwhile, AB InBev shares are more than 35 percent higher than in October.
Aberdeen Asset Management said the revised offer undervalued the company and continued to favor Altria and Bevco, the Santo Domingos’ investment vehicle.
AB InBev said the share-and-cash offer value was now 51.14pounds, so above the 45 pounds of pure cash, but the new shares offered would have to be held for at least five years.
"I wouldn’t like to second guess what the activists were hoping for, but the increase is quite modest," one SABMiller shareholder told Reuters. Liberum analyst Alicia Forry said she believed the revised bid was likely to be successful by throwing a "small bone" to activist investors and shutting the door to further increases.
"The main thing from ABI's perspective is they don't want this to drag and if they engaged (activists) it would," she said.
SABMiller, which provisionally agreed the deal struck in October, said it had taken on Centerview Partners as a new financial advisor and would consult with shareholders before formally considering the revised offer.
The takeover is still awaiting regulatory approval in China. SABMiller shareholders would expect to vote on it after that.
At 1445 GMT, SABMiller shares were down 0.4 percent at 44.20pounds. AB InBev's were up 0.6 percent at 115.50 euros.