I'd assume Guarnier going back on her retirement announcement is because with TIBCO she'll get a US-based calendar and can ride a reduced amount, which is only fair.
Virtu have signed a couple of prominent Italians, WWT U23 winner Sofia Bertizzolo from Astana and veteran sprinter and former World Champion Marta Bastianelli. They've also signed Anouska Koster from WaowDeals, so their squad is starting to look like a genuine threat.
Canyon-SRAM have picked up the two most prominent Israeli cyclists in the pro péloton, Rotem Gafinovitz from WaowDeals and Omer Shapiro from Cylance. Speaking of Cylance, the company will re-enter the péloton, but not as its own team going forward. Canyon have also signed 20-year-old Ella Harris, from New Zealand, via the Zwift Academy.
The general face of the women's pro péloton seems likely to change with the significant changes this off-season. Much as the previously-dominant Rabobank team eventually became too top heavy for its own good, it seems like the domination of Boels may not be quite so outright in the 2019 season as, while they will undoubtedly still win plenty with the extremely strong squad they've got, they may not be quite so dominant as the days where they could stick their whole team into a group of 15 at the end of a major classic may be over. While they've replaced pretty well - they've lost Deignan and Guarnier, they've brought in Hall and d'Hoore - other teams seem to now be strong enough to provide a more significant threat. Mitchelton-Scott already were the biggest threat, with van Vleuten and Spratt, but having lost d'Hoore to Boels they'll be less of a season-long challenge I assume, as they are now almost completely set up with their strongest riders in the hillier and mountainous races. They will also hope Lucy Kennedy can stay healthy for more of 2019 than she managed in 2018. Sunweb may have lost van Dijk and Winder, but they still have Brand, Kirchmann, Rivera and a very strong group of youngsters with Lippert, Labous, Mackaij and Mathiesen, and they've also added Susanne Andersen plus more veteran strength with Janneke Ensing. Canyon are mostly unchanged from last year in terms of their key riders, obviously Niewiadoma is their big threat, depending on if we ever see 2013-14 era PFP again, but also Alexis Ryan and the Barnes sisters will be a year older too and Cecchini has the smarts to maximise results too. But definitely the most on-paper dangerous opposition will be Trek - a brand new team with a formidable leadership group. While Deignan's post-childbirth shape has yet to be determined and how quickly she gets back up to speed is not known, even if she has a slow start to the season, the team already has plenty of sources of results to take the pressure off her, seeing as they also have Elisa Longo Borghini and Ellen van Dijk, just for starters. With Lotta Lepistö as lead sprinter, youth phenom Letizia Paternoster, established veteran road leaders like Audrey Cordon-Ragot and wildcard climbers like Jolanda Neff, their squad looks like it could go straight to the head of the péloton.
Meanwhile, others will undoubtedly be shuffled down the pack. Alé-Cipollini have lost one of their two key sprinters (Bastianelli), their most durable and all-round rider (Ensing) and their strongest GC climber (Santestebán). They've signed some decent riders but not that replace the hole that those three will leave, and they will become fairly heavily reliant on Chloe Hosking for results, I'd wager. Astana losing Paternoster and Bertizzolo more or less tears the strongest future riders out of that team and in fact they now have no Italian base at all. Again, they will become heavily reliant on one rider, Arlenis Sierra on this occasion. Cervélo are the biggest example of this - they have lost a small number of riders and gained many, but that small number of riders included 2 of their 3 main results-getters - Ashleigh Moolman-Pasio, who has gone to CCC-Liv to fill the Niewiadoma-shaped hole in their results from 2017 to 2018, and Lotta Lepistö who moves to Trek. The pressure on Cecilie Uttrup Ludwig to provide the results to plug that gap will be significant, though they have surrounded her with friends and compatriots like Marie Vilmann and hotly-tipped teenager Emma Norsgaard, as well as Czech climber Nikola Nosková, and adding veteran road leader Julie Leth.