How to make a Slavic Pannonian/Carpathian Basin?

What would be required to keep the Pannonian Basin linguistically majority Slavic, with a more-or-less unbroken dialect continuum between West Slavic and South Slavic languages?

The Magyars are pretty easy to remove; have them take a different turn, have them settle somewhere in Russia and get slavicized, have them stay in Wallachia-Moldavia (and get wiped out by the Pechenegs?).

But several threads about Magyar-less Pannonia have posited that the basin would instead be annexed and colonized by Bavarians. How can this be prevented?
 
If you have some POD that depopulates a big chunk of Northern Europe, maybe you can send the extra Germans there instead. IIRC, the Black Death didn't hit the Slavic lands very hard. What if an equivalent plague comes along a few centuries earlier?
 
What would be required to keep the Pannonian Basin linguistically majority Slavic, with a more-or-less unbroken dialect continuum between West Slavic and South Slavic languages?

The Magyars are pretty easy to remove; have them take a different turn, have them settle somewhere in Russia and get slavicized, have them stay in Wallachia-Moldavia (and get wiped out by the Pechenegs?).

But several threads about Magyar-less Pannonia have posited that the basin would instead be annexed and colonized by Bavarians. How can this be prevented?

?
If a sufficiently strong Slaovic state exists, no colonization can succeed - no more than it happened for Poland, at least. Supposing a kingdom centerd in Nitra, *Strigonium/Esztergom of around lake Balaton (which indeed has a Slavic original name, from Blatny), fully Christianized in the XIth century and militarily strong enough to resist encroachment, in the following centuries several German-speaking settlments and cities sprout throughout the basin, but without altering the nation's character in depth.
 
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