<< Tibetan spiritual leader Dalai Lama waves as he leaves Lilavati hospital in Mumbai September 1, 2008. (REUTERS/Punit Paranjpe)

Revered by Tibetan Buddhists as their spiritual leader, but loathed by China as a troublemaking separatist, the Dalai Lama smiled and waved to supporters as he left a hospital in India on Monday after being treated for four days for a stomach ailment.

But questions about the mortality of a man who supporters believe is actually the latest reincarnation of a long line of enlightened masters are now being raised.

There are also questions about who will succeed him as head of Tibet's government-in-exile, as well as the future of the Himalayan region itself.

But they also predict widespread unrest in the region despite Beijing being likely to introduce draconian security measures.

The Dalai Lama's death and the search for his successor could create a rallying point at home for more than 5 million Tibetans, many of whom are unhappy with Communist rule.

"There will definitely be rioting. It'll be a lot bigger in scale than March 14," said Wang Lixiong, Chinese author of three books on Tibet, said, referring to unrest which spilled over into nearby Tibetan populated provinces in March and in ensuing weeks.

Lodi Gyari, the Dalai Lama's envoy in Washington, has warned of potential instability unless the Tibet issue -- an emotive one for many Westerners from the U.S. Congress to Hollywood -- is resolved within the Dalai Lama's lifetime.

"We Tibetans, being pragmatic, will recognize violence will only be a means but not an answer to our struggle," said Khedroob Thondup, a nephew of the Dalai Lama.

Complicating matters is the fact that Beijing will almost certainly appoint its own successor to the Dalai Lama.

"But this will just be futile as the Tibetan people will not recognize him," Khedroob Thondup, a member of Tibet's parliament-in-exile, said in an interview from his home in India.

After the 10th Panchen Lama, Tibetan Buddhism's second most senior figure, died in 1989, Beijing and the Dalai Lama made rival choices for his successor, and the Dalai Lama's choice, then aged six, suddenly disappeared from public view.

Tibetans around the world say he was kidnapped by Chinese authorities and human rights watchdogs have called him the world's youngest political prisoner. China denies the accusations and insists he and his family do not want to be disturbed.

China has defended its rule in Tibet, saying life has improved for most Tibetans since the Dalai Lama fled. China has poured billions of yuan into the Himalayan region and opened a 1,142-km (710-mile) railway linking it to the rest of China.

But the harsh crackdown since March has fuelled a vicious cycle fanning ethnic tensions.

Many exiled Tibetans have clamored for independence and shun the Dalai Lama's "Middle Way" approach that advocates autonomy.

The leadership vacuum in Tibetan Buddhism is tipped by some Tibetologists to be filled by the Karmapa Lama, ranked third in the religion's hierarchy who followed in the Dalai Lama's footsteps and fled into exile in India in 2000.

Another candidate is Yabshi Pan Rinzinwangmo, daughter of the 10th Panchen Lama.

The Central Intelligence Agency trained and provided arms and radio equipment for Tibetan guerrillas fighting the People's Liberation Army from the 1950s to the 1960s, but pulled the plug in 1972 when then U.S. President Richard Nixon visited China.

But the possibility of Tibetans resuming guerrilla warfare in the post-Dalai Lama era is extremely remote without the backing of the United States.

Washington has been a vocal critic of China's human rights record and has urged Beijing to continue dialogue with the Dalai Lama. But it is also is counting on China's help in reining in a nuclear North Korea.

(Editing by Nick Macfie and David Fox)