Just a few points to keep in mind.
1. Unfortunately nothing has yet been found with respect to the Peucini. Particularly after they became the sole carriers of Bastarnian identity. That is the stated view of the respected author of the best book on Chernyakhiv (Borys Mahomedov, writing in 2001), who wished to discover whether any "Bastarnian" elements had contributed to the emergence of classical Gothic material culture. So right now, all we have are historical documents which bring the story up to the end of the 3rd and the beginning of the 4th centuries, when the Peucini became part of the Roman Empire's population in Moesia. That and (perhaps) some surmises.
2. The notion that the northern Bastarnians (Atmoni and Sidones) were (at least to some extent) evicted from their haunts by Burebista has some plausibility. There is no doubt at all that the Poeneshti-Lukashovka culture, now accepted as Bastarnian, ceased to exist in practically all areas where it was identified for the period ca. 200 BCE-ca. 50 BCE. But the notion that they migrated to Poland and Germany and became a new "upper class" there has no archaeological backing at all. For the simple reason that we now know what happened to them (at least to a very lage part of them).
3. When Rolf Hachmann and Ion Horatiu Crishan published their studies (in 1961 and 1978) it was believed that Poeneshti-Lukashovka "died" at the latest in ca. 50 BCE (and for Hachmann even earlier I believe, in the 70's BCE). The work of a number of Ukrainian archaeologists has overturned this. B. Timoschuk and I. Vynokur discovered a large number of settlements in the area of Bukovyna (today's Chernivtsi region of Ukraine) and even in southeastern Galicia, which C. Pachkova subsequently identified, quite convincingly, as Poeneshti-Lukashovka. Since 1978 (when Pachkova's first article appeared) there is no doubt that a "late phase" of Poeneshti-Lukashovka existed north of their previous haunts, at more than 40 locations. Some were also found considerably to the south (at Perkari close to the Dnister delta), indicating that the migrating Bastarnians sought "freedom" from Burebista not only in the north but also close to their
Peucinian associates. All these settlements existed in the period ca. 50 BCE (or a little earlier) to the end of the 1rst c. BCE and into the first decades of the 1rst c. CE. We know of some142 Poeneshti-Lukashovka locations (not all existed simultaneously) for the period 200-50 BCE in the traditional Moldavian Poeneshti-Lukashovka area. So the 40+ locations of Bukovyna/Galicia testify to a pretty large population.
4. What happened after ca. 1-20 CE? Since there is no evidence anywhere else, one plausible surmise is that these late northern Bastarnians migrated towards Peuca, and fused with their brethren there. There are other possibilities. But neither I nor anyone else knows of any evidence which would place Bastarnians in the Przeworsk culture area at that time as a new "ruling class". The archaeology of Przeworsk has no discernible Poeneshti-Lukashovka features for that period. And one should also note that the burial rite of the classical as well as "late" Poeneshti Lukashovka was that of cremation. Exclusively.
5. One interesting point about the area to which Bastarnians fled from Burebista (Bukovyna/Galicia). Timoschuk discovered an early settlement there (Horoshova, dated from the late 3rd c. BCE) which existed just prior to the emergence of Poeneshti-Lukashovka further south. As is well known, Poe./Luk. is a composite culture which allies local Getic cultural (substrate) traits with incoming Celto/Germanic (especially Yastorf) ones. The settlement in question was Yastorf/Pomorian only (no Getic traits at all). Which suggests that the Atmoni and Sidones retreated to an area they had first settled upon arriving from the north.