I'd go for the clearest immediate cause of the collapse: the
Mycenaeans. One can leave it vague as to whether one regards them as the
sole cause, or are postulating some sort of resurgence after other
difficulties are overcome, which (on this hypothesis) the Mycenaeans
exploited. It will make no real difference to the overall shape of
events.
So, eliminate the appearance of Mycenaean Greeks in Crete. How?
We know very little here, so a simple POD seems safest. Let's suppose
that the Minoans have a strong enough navy in this TL to keep the
Mycenaeans out. As a result, the age of the great palaces continues,
perhaps after a period of troubles.
In the interests of keeping the AH controllable, I propose that we
allow Mycenaean civilization to take much the same course as in OTL. Note
that this, in the current state of our knowledge of the later 2nd
millenium, needn't be unrealistic. One can postulate vast unspecified
differences from the political events of OTL, without it having to bother
us, since we don't know anything about this anyway. There's no reason to
suppose that any such effects of Minoan survival have to save Mycenaean
civilization from its collapse, an event whose causes are extremely
obscure.
It is at this point that one hits the first significant crux.
Does Minoan civilization share in the Mycenaean collapse? I'd say not,
because if it does the AH fizzles out here: Crete is overrun by Mycenaean
migrants as in OTL and the alternate TL rejoins the real one. How does
Crete avoid this fate? Let's go for the strong navy option again. For
color, one can combine this with the adoption of the Mycenaean-style
fortified palace, ironically at the very point at which it is being
abandoned by the Mycenaean Greeks themselves.
We're now at a stage where possible divergences start to become
obvious. If the Minoans can keep the Greeks out of Crete, then they can
probably also keep them out of the Cyclades. That inhibits the whole
eastward migration of Mycenaeans to Asia Minor in this period. So the
same movements of peoples are directed towards the west in this TL
(following up on established Mycenaean contacts). Instead of Ionia, we
have an earlier Greek Sicily and South Italy at the beginning.
Note that, with no Ionia, Archaic Greek contacts with the Middle
East will be mediated overwhelmingly through the Minoan palace culture.
One would speak of a "Minoanizing" rather than an orientalizing period in
Greek pottery. The Minoans themselves have opportunities for great
commercial wealth as middlemen. I think it was suggested at one point
that the Minoans and Phoenicians might ally. The Minoan economic interest
in keeping the Phoenicians out of their sphere seems to me to be so strong
that a hostile relationship is more probable. Phoenician-Greek contact
will be normal only in the western Med. (As a consolation prize, the
Phoenicians get to dominate Cyprus in this TL).
Minoan cultural continuity presumably includes Linear A.
Therefore, the reintroduction of writing into Greece will be in the form
of a Linear A-derived script we might call Linear C (probably not too
different from Linear B). Other Minoan cultural imports would be
particularly prominent in the areas of religion and mythology. The
Minoans, due to geographical proximity, would also be the quintessential
"foreigners" against whom an emerging sense of "Greekness" would define
itself: palace vs. polis at a minimum, perhaps also matriarchy vs.
patriarchy, and (in contrast with OTL) the Minoan sailor vs. the Greek
landsman. A collective Greek identity would emerge earlier.
The emergence of the Ionian thinkers is striking enough that I
suspect it depended on a particular combination of circumstances, one of
which was almost certainly the variety and depth of contacts with the
Middle East. So IMO it is reasonable to say that Greek philosophy and
rationalism will very likely not develop in this TL.
What happens when the pressures that lead to Greek colonization in
OTL build up? The best sites in the west are taken. The Minoans block
the east. The result is probably a) even more political upheaval among
the Greeks, with earlier tyrannies, some of whom, influenced by the
Minoans, may try to establish palace-based systems and b) conflict with
the Minoans, as the Greeks try to open up routes to Asia Minor and the
Black Sea. In the later stages of this process, accommodating the demands
of hoplite warfare is likely to prove a strain on the Minoan system.
Rather than drastically reorganize their social structure, they are likely
to fall back on the use of Greek hoplite mercenaries. (There are other
options, but Minoan civilization is looking so very static at this point
that I think one has to build in a marked preference for the most
conservative choice). Reliance on mercenaries proves futile when the
Greeks deprive the Minoans of their naval dominance (say, around 600 B.C.)
and thus of the commercial position on which their wealth is based.
Economic collapse provokes social crisis, and the palace civilization
breaks down. By 400 B.C., the palaces have been abandoned, except as
religious sites, and the towns have transformed themselves into
Greek-influenced city-states. Minoan language and culture remain the norm
on Crete and the Aegean islands, however. For color, one can say that an
isolated palace administration survives on Rhodes.