I suspect that our current targets such as Lacazette and Lemar/Mahrez are based upon the premise of Sanchez remaining at the club. Essentially they are to compliment Sanchez as being the focal point of the attack. I do not think that the pursuit of Mbappe is anything more than a distraction for the probable departure of Sanchez this summer, as a supposed show of ambition and intent in the market. I also think that retaining the 3 at the back minimises/eliminates the need to address the midfield.
That said I suspect that Lacazette is fast approaching a point re his transfer fee where he costs more than the potential market value for Sanchez, at which point I'd be expecting AW to look elsewhere as he did previously re Jovetic-Higuain-Suarez, except this time I'd hope that he'd learned his lesson about splitting hairs on fees and ending up empty handed. If we are to consider upgrades from Lacazette then it should include the likes of Aubameyang, Icardi, Cavani, Mandzukic, Aguero.
Should Sanchez depart then we should re evaluate our targets accordingly. As such we either need to improve our intended targets at CF and AM/WF, and/or we should look to replace Sanchez with similar quality/capability - James, Dybala.
If we are unable to secure top level targets at CF, AM/WF we should consider looking to sign a top level CM to play alongside Xhaka in addition to our replacements at CF & AM - Nainggolan, Milinkovic-Savic, Goretzka, Jorginho, Seri.
The more players we look to sign then the higher the quality and/or the more important PL experience, so as to minimise adaption time.
Best case scenario losing Sanchez & not signing Mbappe, but willing to spend the same level of funds could be something like:
Aubameyang
James - Ozil
Lemar - Xhaka - CM - Bellerin
Kolasanic - Kos - Mustafi
Cech/Butland
Worst case scenario based upon losing Sanchez & unable to sign our preferred targets at CF & AM/WF, should/could be something like:
Aguero
Martial - Ozil
Kolasanic - Xhaka - Rambo - Bellerin
Kos - BFG - Mustafi
Cech/Butland
alternatively
Aguero
Martial - Ozil - Mahrez
Xhaka - CM
Kolasanic - Kos - Mustafi - Bellerin
Cech/Butland
